Update to libc 0.2, remove unnecessary gl_common crate

[mitchmindtree]

I thought I'd open up another PR branch (an alternative to #655) that attempts to update to libc 0.2 and removes the gl_common dependency.

This build succeeds locally on OSX.

@tomaka I don't have a thorough understanding on what gl_common's original role was, however I noticed that you recently removed it from gl-rs, so I thought it might no longer have a place here - let me know if I was wrong and this should be done another way!

[tomaka]

Conflicts a bit with #652

gl_common was meant to provide a way to replace load_with(|s| window.get_proc_address(s)) with
load(window).

[mitchmindtree]

Ahh, wasn't sure if you were still going ahead with #652 - perhaps I should close this and you can go ahead and do this within #652? It seems the libc update and gl_common fixes would need to happen in the same PR.

[tomaka]

I merged your stuff in #652