Implement #188
Put back original rust-xml location
Merge pull request #195 from tomaka/master

Put back original rust-xml location
Update token capitalization & usage

Upstream changes to naming / tokenizing made things easier, but
necessitated changing the token analysis code. Some legacy manual
span analysis code may still exist.
Merge pull request #196 from mcoffin/token_conventions_nightly

Update token capitalization & usage
Use TokenTree::get_span
Clean up delimiter matching
Merge pull request #198 from bjz/generator-cleanups

Generator cleanups
Change fail! to panic!
Merge pull request #199 from lucidd/master

Change fail! to panic!
Update for rustc
Merge pull request #200 from tomaka/master

Update for rustc
Update examples

Closes #194
Merge pull request #201 from bjz/update-examples

Update examples
Update token tree
Update lints
Merge pull request #202 from bjz/update-token-tree

Update token tree
Updated README to reflect changes in glfw-rs.
Merge pull request #203 from Minalien/master

Updated README to reflect changes in glfw-rs.
gl_generator: implement fallbacks based on aliases

These aliases are already present in the XML, so we might as well use them! As
OpenGL evolves and is extended, it frequently occurs that a vendor introduces
an extension, giving a function a name like `glFooNV` or `glFooAMD`. Then, it
gets proposed to the ARB and is renamed `glFooEXT`. Then, this extension gets
standardized and is placed in the core profile and is once again renamed to
its final name, `glFoo`.

For Mesa, they implement various extensions and then finally support an OpenGL
version once all extensions have been implemented. Many OpenGL features can be
implemented entirely in the driver, or on most hardware even if the hardware
doesn't support enough features for a specific OpenGL version. So you get
situations where older GPUs only expose OpenGL 2.1, but implement almost every
extension that is present in OpenGL 3.3.

So, when `glFoo` can't be loaded but it has known aliases, try also loading
those aliases before giving up.

Closes #150