rename tree.py to Tree.py
gitignore
use mpi4py instead of boostmpi (as recommended by the maintainer of the latter)
include pyglog (no longer available at URL provided)
reduce footprint of NLPTree initialization
avoid costly regular expressions
faster insert at end of list
avoid (costly) Tree.bottomup() generator
remove unused variables
only make deep copy of tree if it is being used (dunno if all deep copies are necessary)
pure python vector instead of svector (which keeps eating memory)
breaks loading of models trained before this commit!

Nile can now be run with PyPy (3x speed-up)
use json for weight storing/loading for transparency/compatibility.
breaks loading of models trained with previous versions!
with json serialisation, future changes of weights object will be backwards-compatible.