 add `EXT_color_buffer_float`, `WEBGL_compressed_texture_s3tc_srgb`, and  `EXT_disjoint_timer_query_webgl2` to `twgl.addExtensionsToContext`.
 add `EXT_color_buffer_float`, `WEBGL_compressed_texture_s3tc_srgb`, and
 `EXT_disjoint_timer_query_webgl2` to `twgl.addExtensionsToContext`.

greggman/twgl.js,greggman/twgl.js,greggman/twgl.js