Grand rename of cwipc point cloud object and C function names?

[jackjansen]

We should we bite the bullet and get rid of the cwipc object, renaming it to cwipc_pointcloud. The current double meaning of cwipc (some places it signals the whole package, in other places it is the point cloud object) is pretty confusing.

And, in a similar vein, we should rename all the C functions so that if they have a first argument that is really an object/class instance this is reflected in the name. So, cwipc_get() would be renamed to cwipc_source_get().

Note that this has very limited effect on the Python and C# interfaces, because these duplicate the C++ interface (vectored through the C interface).