Add library routines for finding, selecting Text Objects

[jrk]

Vim's block navigation and selection commands (inner and outer block, (, {, etc.) are very powerful, especially as modifiers to editing operations.

These might be possible to implement entirely as macros of Ruby => NSResponder methods (especially relying on marks), or it might be best achieved via a low-level Objective-C extension.

[philc]

Unfortunately, TextMate's OakTextView doesn't implement marks, although there may exist methods in TextMate's class hierarchy which allow us to select the surrounding scopes.