split out knn search functions
simplify mask handling a tiny bit
_parse_specs: handle alphas by partialling things, support chooser_func
actually, partial in the Ks also
alpha_div: precalculate the constants that are always the same
move base estimators to their own file
move the core of estimate_divs into that file too

next step: cython this all
partial on the dimension, also; pre-compute linear's constants
whoops, remove dead code
avoid a copy when we can
minor clarity tweak
don't unnecessarily pre-group the nus
remove dead code
we actually require pyflann now, not just encourage it
knn_search: return float32 by default
move non-cythonning stuff back into np_divs.py
cython up _np_divs. it works!
open-mp the cythonned estimators
whoops, messed up setup.py cython check
whoops, guess i didn't test that...