Correct cross reference for timing.

 * * @ref jit Generic interface for Just-In-Time compiling of the graphs.

 * * @ref backend Host side buffers and operations.

 * * @ref gpu Device drivers for CPU and the GPU.

 * * @ref timeing Routines for timing.

 * * @ref timing Routines for timing.

 * * @ref output Routines for loading and saving graph to Netcdf files.

 * * @ref commandline Routines for parsing command lines.

 *