Changes to include this library in servo

We are students from NCSU working on the project https://github.com/servo/servo/wiki/Replace-C-libraries-student-project

We are attempting to replace the [rust-freetype](https://github.com/servo/rust-freetype) library used in [servo](https://github.com/servo/servo) with freetype-rs.

We did not find support for Truetype fonts in freetype-rs, and have ported some code from rust-freetype.
Let us know if these changes are good enough to be pulled into freetype-rs.