Fix CMAKE_FIND_ROOT_PATH

This allows projects and libraries using CMake to automatically find include directories and library files in the emscripten system directory. I am unsure why it was set to `${EMSCRIPTEN_ROOT_PATH}/cmake` before, but I tested it and it didn't work until I changed `cmake` to `system`. `CMAKE_FIND_ROOT_PATH` is documented [here](http://www.cmake.org/Wiki/CMake_Cross_Compiling#Searching_and_finding_external_software).
Refactor sdl_canvas_size

There's no need to load all the OpenGL stuff to
test canvas size and resizing.
add SDL_GetRGB and SDL_GetRGBA
add SDL_putenv
add myself to AUTHORS
Merge pull request #2459 from jonessen96/fix-cmake

Fix CMAKE_FIND_ROOT_PATH
Don't increment result, return 1 on success or 0 on failure
Merge pull request #2460 from gsathya/clean_canvas_size

Refactor sdl_canvas_size
assert on memory initializer region not being written to before it is applied
add assertions on the runtime being ready before using ccall/cwrap
suppress runDep recurring listing if aborted
clear runtimeInitialized in exitRuntime, to assert on runtime usage after exiting
use navigator.hardwareConcurrency for sysconf(SC_NPROCESSORS_ONLN); fixes #2456
fix uninitialized structure data in ignored touchmove events; fixes #2466
make sure worker waits for pre-proxy info before starting up, and some proxy protocol fixes
Added CMAKE_FIND_ROOT_PATH test
Merge pull request #2467 from jonessen96/fix-cmake

Add CMAKE_FIND_ROOT_PATH test
add COMPRESSED_TEXTURE_FORMATS to prefetched gl parameters
Merge branch 'sdl' of github.com:sronsse/emscripten into incoming

Conflicts:
	AUTHORS
fix browser.test_mem_init