Implement struct loader generator.

I am getting this error:

~~~
src/examples/struct_triangle.rs:30:5: 30:17 error: unresolved import
src/examples/struct_triangle.rs:30 use self::gl::Gl;
                                       ^~~~~~~~~~~~
src/examples/struct_triangle.rs:36:9: 36:13 error: unresolved import (maybe you meant `libc::*`?)
src/examples/struct_triangle.rs:36     use libc;
                                           ^~~~
~~~

:(