Add GLEW 1.10.0 emulation

Includes library_glew.js that stubs the init functions, but also provides the
other functions.

GL/glew.h is now changed to work with GLEW_EXT_foo_bar constants,
some missing constants that are in GLEW 1.10.0 are also provided.

Otherwise it still uses SDL_opengl.h to provide function definitions and
other constants.

Linaro's GLEW (glew-oes) is also supported to some degree to make it
easier to get ES1 and ES2 software using it running.

What it lacks:
- Some constants and function declarations that are in GLEW 1.10.0
might be missing.
- The real glew-es fork also includes normal GL constants and
function pointers, this does not.

Tests ran:
- tests/runner.py browser

Real world example using this code (and upcomming glfw3 port) can be found here:
http://cloudef.eu/glhck