MacPlatform: support TextMate compatible URIs

Implements support for a monodevelop:// URI scheme
that is compatible with the TextMate scheme:

  - http://blog.macromates.com/2007/the-textmate-url-scheme/

Example:

  - $ open 'monodevelop://open?file=file:///Users/aaron/foo.cs&line=25&column=10'