First attempt at wrapping dsift

Builds, but totally untested. Also, pretty irritating that we
are going to have to replicate the Makefile logic. However,
the other option might be to create 'built' packages for
vlfeat...
Fix the dsift version so that it matches Matlab

Still needs commenting to explain some of the decisions that
were made
Accidentally commited annotations
Comment code in cython

Try to explain the dsift code a bit better within the Cython