Added glDepthFunc, glDepthMask and StencilFunction consts.
Added delete functions
Added glActiveTexture and consts
Added blend functions and constants
Merge pull request #7 from sethpink/more_funcs_2

Added glDepthFunc, glDepthMask and StencilFunction consts.
Added get_program_info_log
Merge branch 'master' of github.com:Jeaye/rust-opengles