Added global config directory

+ Should be platform independent thanks to platform-dirs
+ All config files in the directory are used
+ Some optimizations could be made so now all config files are loaded.
+ clippy + fmt

src/main.rs

@@ -22,6 +22,15 @@ pub struct Args {
     )]
     config: Option<PathBuf>,
 
+    #[structopt(
+        short = "g",
+        long = "global_config",
+        env = "FORMATY_GLOBAL_CONFIG",
+        parse(from_os_str),
+        help = "Path to the global config directory"
+    )]
+    global_config: Option<PathBuf>,
+
     #[structopt(
         help = "Input data type",
         short = "i",
@@ -43,7 +52,7 @@ pub struct Args {
 fn init() -> Result<(Vec<u8>, Format), FormatyError> {
     let args: Args = Args::from_args();
 
-    let config = FormatConfig::new(&args.config)?;
+    let config = FormatConfig::new(&args.config, &args.global_config)?;
 
     let format = config.get_format(&args.format)?;