improve the -help command

[michael-je]

I think the command should be improved in the following ways:

• when using the command as -help <command name> the user should get a more detailed description than the short one presented when using -help.
• some commands are very multifunctional. For example, -play can be used as is to to resume playback if paused, or with arguments to queue up a song using either a url or search term, or queue a playlist. I think that it should be possible to give each argument type its own short description to make the functionality more clear, something like:

-play           resume playback if paused
-play <url>     play a song or playlist with a url
-play <term>    play a song using a search term