[MATLAB] fix problem in typecheck for passing mxArray (was still using Octave classes)
[MATLAB] emit autodoc for functions

Octave allows storing documentatino via texinfo in the .oct file, but matlab doesn't.
Therefore, the code was changed to write documentation strings in the .m files.
This is currently only done for functions.

As a cleanup, the "docs" hash has been removed. The autodoc strings are now
stored as attributes attached to the original node (e.g. "matlab:synopsis").