Towards v0.2.4

This request contains a variety of changes.  First off, in preparation for allowing quantities to be integrated across surfaces in real-time the MPI{Matrix,View} classes have been renamed to Xchg{Matrix,View}. 

In response to an issue identified by Zach Davis the clBLAS wrappers now also give the error status code when an exception is raised.

The main improvement is preliminary (read: test me!) support for surface anti-aliasing.  Some of the code is a little rough around the edges but the principle seems sound.  In the process some bits of code have been re-factored: the confusing fbasis is now the gbasis (g = correction function) and the need to prefix quadrature rule points/weights by `np_` has been eliminated.  This may break some scripts which use the quadrature rule getting functionality of PyFR.  Removing the prefix should resolve the issue.