Bugfix: Fixed incorrect return type to *RngState.
Added gsl wrappers for quasirandom sequences.
Removed call to SetFinalizer in alloc routines.

It seems that go calls the finalizer functions
prematurely (well at least before I think it should
call them) causing segfaults in libgsl. So I removed
the cals to SetFinalizer. Instead I added an explicit method
Free() to release the underlying memory in libgsl.