Make config arguments globally available on all commands (#326)

Fixes #325

src/config.rs

@@ -8,12 +8,13 @@ pub struct FnmConfig {
     #[structopt(
         long,
         env = "FNM_NODE_DIST_MIRROR",
-        default_value = "https://nodejs.org/dist"
+        default_value = "https://nodejs.org/dist",
+        global = true
     )]
     pub node_dist_mirror: reqwest::Url,
 
     /// The root directory of fnm installations.
-    #[structopt(long = "fnm-dir", env = "FNM_DIR")]
+    #[structopt(long = "fnm-dir", env = "FNM_DIR", global = true)]
     pub base_dir: Option<std::path::PathBuf>,
 
     /// Where the current node version link is stored.
@@ -28,7 +29,7 @@ pub struct FnmConfig {
     multishell_path: Option<std::path::PathBuf>,
 
     /// The log level of fnm commands
-    #[structopt(long, env = "FNM_LOGLEVEL", default_value = "info")]
+    #[structopt(long, env = "FNM_LOGLEVEL", default_value = "info", global = true)]
     log_level: LogLevel,
 }