function getWebGLContext(canvas, opt_attribs) {
    var gl = create3DContext(canvas, opt_attribs);
    addVertexArrayObjectSupport(gl);
    return gl;
  }
Gets a WebGL context.
@param {HTMLCanvasElement} canvas a canvas element.
@param {WebGLContextCreationAttirbutes} [opt_attribs] optional webgl context creation attributes
@memberOf module:twgl