support android build
add android main
add some android port materials into gfx
hybrid window system - glut for android and glfw for others
fix dom bindings for android(and 32bit system) build
fix compile err (internal compiler err on ARM)
update submodules
add native submodules for android
add rust-glut for android
fix Mac build
auto merge of #724 : webconv/servo/androidport, r=metajack

Works of android port.

Notices.
1. added more native submodules - libpng, libfreetype2, libfontconfig, libexpat (currently, they are on our repo)
2. build directory change : [build directory]/[XXXX] -> [build dir]/[target triples]/[XXXX]
3. added android main
4. uses freeGLUT instead of GLFW on android
4. fixed misc.

Usage: configure --target-triples=arm-linux-androideabi && make
Result: cross-compiled 32-bit so libraries.