moved is_terminal to FunctionNode. A FunctionNode is a terminal if it doesn't contain any FunctionNodes below
fixed is_terminal again
fixed depth problem in increment_tree, fixed corner case in FunctionNode.is_terminal
Fixed insanely subtle bug in Grammar -- x in a lambda overwrote x in outer scope
changed depth accounting
made MHSample compute the posterior of h0, changed make_h0 in number to accept a value; working version of PartitionSpace
optimizations for performance evalaution
reverted back how depth is measured in enumerate -- the old way was better
removed Number bits
small fixes
Merge branch 'master' of https://github.com/piantado/LOTlib

Conflicts:
	LOTlib/Grammar.py