LIC : change license from GPL -> 3 clause BSD

They promised me cookies!
DOC: Update walkthrough tutorial to latest PIMS and trackpy API.

More work needed -- should mention new features --
but there is nothing incorrect here.
Merge pull request #84 from danielballan/tutorial-update

DOC: Update walkthrough tutorial to latest pims and trackpy API.
BUG/PERF: Re-enabled loop short-circuiting in _refine_numba() by fixing typo.
Merge pull request #86 from nkeim/numba-refine-cleanup

BUG/PERF: Re-enabled loop short-circuiting in _refine_numba()
Merge pull request #46 from tacaswell/lic

LIC : change license from GPL -> 3 clause BSD
TST: Test several flat peaks where duplicates should be merged.
PERF: Refactor flat peak duplicate merging and margin detection.
CLN/BLD: No more C extensions.
PERF: new benchmark targeting local_maxima
Merge pull request #85 from danielballan/secondary-maxima

Secondary maxima
REF/API: numba is enabled only for v0.11 and waits to compile
BLD: Add a numba 0.12 (numpy 1.8) build.
Merge pull request #83 from danielballan/avoid-slow-import

REF/API: numba decorators only turn on for numba 0.11.*