Utility functions

[Yoric]

A few utility functions that I use in my implementation of ropes.
I will send a separate pull request for ropes once I have finished cleaning up the code.

[Yoric]

Ah, well, I have finally decided to add the library to the pull request.

[Yoric]

I should add that this library is my first real foray into Rust. I fully expect numerous efficiencies, unexpected memory copies, etc. Please do not hesitate to point me to any error I may have committed.

[Yoric]

Actually, there is a difference between loop_chars and iter_chars: the second cannot be interrupted.

[brson]

So this looks really great! Thank you. I made a number of comments, but mostly on style. One thing to note is that functions without naturaldocs comments (starting with "Function:") will not show up in the library documentation at all, so every public function needs documentation.

This patch does establish a naming convention 'loop' and a protocol (return bool) for iterators that can break early, which I guess is as good as any.

I would very much like it if you provided tests for std::rope. They would live in src/test/stdtest/rope.rs

[Yoric]

Normally, everything is done, except for the explicit export in rope.rs, which I still need to ponder.

[brson]

Thanks, Yoric. Integrated.