pep8 fixes

Conflicts:
	trackpy/tracking.py
non-recursive working, but slower on tests

Conflicts:
	trackpy/tracking.py
fixed bug in non-recursive tracking that was not properly accounting for
the penalty for not making the maximum number of links

Conflicts:
	trackpy/tracking.py
non-recursive is still significantly slower than recursive version, but
slightly faster

Conflicts:
	trackpy/tracking.py
more incremental improvements

Conflicts:
	trackpy/tracking.py

Conflicts:
	trackpy/tracking.py
change from list -> deque for non-recursive

Conflicts:
	trackpy/tracking.py

Conflicts:
	trackpy/tracking.py
major speed up from sorting the source list by the number of
candidate connections.

Conflicts:
	trackpy/tracking.py
pep8 fixes, removed un-used variable