Document code, fixes #3

src/support_cmd.rs

@@ -1,3 +1,5 @@
+//! Helper functions for invoking system commands.
+
 use errors::*;
 use glib;
 use prefs::Prefs;
@@ -6,6 +8,9 @@ use std;
 
 
 
+/// Execute an available volume control command asynchronously, starting with
+/// the preferences and using some fallback values. If none of these
+/// are valid executables in `$PATH`, then return `Err(err)`.
 pub fn execute_vol_control_command(prefs: &Prefs) -> Result<()> {
     let m_cmd = prefs.get_avail_vol_control_cmd();
 
@@ -16,6 +21,7 @@ pub fn execute_vol_control_command(prefs: &Prefs) -> Result<()> {
 }
 
 
+/// Try to execute the given command asynchronously via gtk.
 pub fn execute_command(cmd: &str) -> Result<()> {
     return glib::spawn_command_line_async(cmd)
                .map_err(|e| {