some playing with python
more python wrapper
lazy eval python wrapper works

still no h2o, but lazy eval  & ref-cnt delete all work
cleanup & comments, more 'pythonic'
more cleanup, prep for next go...
Python wrapper does aggressive temp cleanup

Spot temps in large calculations; inform cluster of all expressions &
temps needed all at once; cleanup after self
Support small-data result of a lazy big-data

mean(x+y) is lazy small result of lazy big result
Split user examples frmo frame.py

Rename frame.py as h2o.py
One more py cleanup

Vecs are thin pointers over Exprs.
Vecs are used to track py-visible pointers to big data; when a Vec goes
dead then the py interpreter cannot "resurrect" a big data pointer.
Exprs holds the Big Data keys themselves dirctly; when they go dead the
Key can be deleted from the cluster.  Also, known-temp values (because
Vecs went dead) are flagged so complex expressions can optimize internal
temps
Gather temps & deletes in same whole expr
Bunch more error checking; allow local data Frames to be made
Begin connecting to a h2o cluster for frame requests
Merge branch 'master' into cliffc-py