Update directories (to 1.0)

Cargo.lock

 dependencies = [
  "cgmath 0.16.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "clap 2.32.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "directories 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "env_logger 0.5.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "directories 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "env_logger 0.5.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "gl 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "gl_generator 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "glutin 0.18.0 (registry+https://github.com/rust-lang/crates.io-index)",
 
 [[package]]
 name = "directories"
-version = "0.10.0"
+version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
+ "libc 0.2.42 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 
 [[package]]
 name = "env_logger"
-version = "0.5.11"
+version = "0.5.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
 "checksum crossbeam-utils 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "2760899e32a1d58d5abb31129f8fae5de75220bc2176e77ff7c627ae45c918d9"
 "checksum crossbeam-utils 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "d636a8b3bcc1b409d7ffd3facef8f21dcb4009626adbd0c5e6c4305c07253c7b"
 "checksum deflate 0.7.18 (registry+https://github.com/rust-lang/crates.io-index)" = "32c8120d981901a9970a3a1c97cf8b630e0fa8c3ca31e75b6fd6fd5f9f427b31"
-"checksum directories 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc2561db021b6f1321d0f16b67ed28ce843ef4610dfaa432e3ffa2e8a3050ebf"
+"checksum directories 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b106a38a9bf6c763c6c2e2c3332ab7635da453a68a6babca776386b3b287d338"
 "checksum dlib 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "77e51249a9d823a4cb79e3eca6dcd756153e8ed0157b6c04775d04bf1b13b76a"
 "checksum downcast-rs 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "18df8ce4470c189d18aa926022da57544f31e154631eb4cfe796aea97051fe6c"
 "checksum dtoa 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "6d301140eb411af13d3115f9a562c85cc6b541ade9dfa314132244aaee7489dd"
 "checksum either 1.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3be565ca5c557d7f59e7cfcf1844f9e3033650c929c6566f511e8005f205c1d0"
 "checksum encoding_rs 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)" = "98fd0f24d1fb71a4a6b9330c8ca04cbd4e7cc5d846b54ca74ff376bc7c9f798d"
-"checksum env_logger 0.5.11 (registry+https://github.com/rust-lang/crates.io-index)" = "7873e292d20e8778f951278972596b3df36ac72a65c5b406f6d4961070a870c1"
+"checksum env_logger 0.5.12 (registry+https://github.com/rust-lang/crates.io-index)" = "f4d7e69c283751083d53d01eac767407343b8b69c4bd70058e08adc2637cb257"
 "checksum flate2 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "37847f133aae7acf82bb9577ccd8bda241df836787642654286e79679826a54b"
 "checksum foreign-types 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f6f339eb8adc052cd2ca78910fda869aefa38d22d5cb648e6485e4d3fc06f3b1"
 "checksum foreign-types-shared 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "00b0228411908ca8685dba7fc2cdd70ec9990a6e753e89b6ac91a84c40fbaf4b"

Cargo.toml

 [dependencies]
 cgmath = "0.16"
 clap = "2.29"
-directories = "0.10"
+directories = "1.0"
 env_logger = "0.5.0-rc.2"
 gl = "0.10"
 glutin = "0.18"

src/config.rs

 static DEFAULT_TILE_SOURCES: &'static str = include_str!("../default_tile_sources.toml");
 
 lazy_static! {
-    static ref PROJ_DIRS: ProjectDirs = ProjectDirs::from("", "", "DeltaMap");
+    static ref PROJ_DIRS: Option<ProjectDirs> = ProjectDirs::from("", "", "DeltaMap");
+}
+
+fn proj_dirs_result() -> Result<&'static ProjectDirs, String> {
+    PROJ_DIRS.as_ref().ok_or_else(|| "could not retrieve project directories".to_string())
 }
 
 
     }
 
     fn find_or_create() -> Result<Config, String> {
-        let config_dir = PROJ_DIRS.config_dir();
+        let config_dir = proj_dirs_result()?.config_dir();
         let config_file = {
             let mut path = PathBuf::from(config_dir);
             path.push("config.toml");
     }
 
     fn add_tile_sources_from_default_or_create(&mut self) -> Result<(), String> {
-        let config_dir = PROJ_DIRS.config_dir();
+        let config_dir = proj_dirs_result()?.config_dir();
         let sources_file = {
             let mut path = PathBuf::from(config_dir);
             path.push("tile_sources.toml");
         }
     }
 
-    /// Returns a tile cache directory path at a standard location. The returned path may not
-    /// exist.
-    fn default_tile_cache_dir() -> PathBuf {
-        let mut path = PathBuf::from(PROJ_DIRS.cache_dir());
-        path.push("tiles");
-        path
-    }
-
     fn from_toml_str<P: AsRef<Path>>(toml_str: &str, config_path: Option<P>) -> Result<Config, String> {
         match toml_str.parse::<Value>() {
             Ok(Value::Table(ref table)) => {
                                    .ok_or_else(|| "tile_cache_dir has to be a string".to_string())?
                             )
                         },
-                        None => Config::default_tile_cache_dir(),
+                        None => {
+                            let mut path = PathBuf::from(proj_dirs_result()?.cache_dir());
+                            path.push("tiles");
+                            path
+                        },
                     }
                 };
 
 
 pub fn read_last_session() -> Result<Session, String> {
     let session_path = {
-        let config_dir = PROJ_DIRS.config_dir();
+        let config_dir = proj_dirs_result()?.config_dir();
         let mut path = PathBuf::from(config_dir);
         path.push("last_session.toml");
         path
 
 pub fn save_session(session: &Session) -> Result<(), String>
 {
-    let config_dir = PROJ_DIRS.config_dir();
+    let config_dir = proj_dirs_result()?.config_dir();
     let session_path = {
         let mut path = PathBuf::from(config_dir);
         path.push("last_session.toml");