Add support to Gamma Correction

[Gustavo Guimaraes]

Gamma correction does not work even on phones that was supposed to support it.

[Alex Szpakowski]

love currently relies on the window manager / graphics driver exposing sRGB back buffer formats, for gamma correction to work. macOS, Linux, Windows, and iOS all support this but most or all Android devices don't. For love 0.11 I'm looking into some workarounds (e.g. issue #1101).