Add declarations for new HTML5 functions emscripten_webgl_create_context(), emscripten_webgl_make_context_current(), emscripten_webgl_get_current_context(), emscripten_webgl_destroy_context() and emscripten_webgl_enable_extension() and a type structure EmscriptenWebGLContextAttributes. Yet unimplemented.
Clarify what target=0 means for emscripten_webgl_create_context().
Add api function declaration emscripten_webgl_init_context_attributes().
Document default values for WebGL context creation functionality.
Add struct fields for EmscriptenWebGLContextAttributes.
Implement HTML5 WebGL context creation API. Add support to library_gl.js to manage multiple simultaneous GL contexts.
Add test for HTML5 WebGL context creation.
Merge pull request #2583 from juj/emscripten_webgl_context

Emscripten webgl context