function getBytesPerElementForInternalFormat(internalFormat, type) {
	    var info = textureInternalFormatInfo[internalFormat];
	    if (!info) {
	      throw "unknown internal format";
	    }
	    var bytesPerElement = info.bytesPerElementMap[type];
	    if (bytesPerElement === undefined) {
	      throw "unknown internal format";
	    }
	    return bytesPerElement;
	  }
Gets the number of bytes per element for a given internalFormat / type
@param {number} internalFormat The internalFormat parameter from texImage2D etc..
@param {number} type The type parameter for texImage2D etc..
@return {number} the number of bytes per element for the given internalFormat, type combo
@memberOf module:twgl/textures