experimenting with different learning algorithms from sklearn
see if presence of more zeros and ones causes overfit
passing the same relation instead of all 26 ones
to see if it fixes learning (it didn't)
trying interpolation instead of regression
found a nice way to handle composition
using a different plot setting
Add a supplemental fact
some experiments
relation formulas 2014
general clean up
Re-add the separate Forward and Backward agents
Merge github.com:opencog/opencog
Remove two dead data files.
Merge pull request #513 from linas/learn

Remove two dead data files.
Shared objects should store use count with this.

I somehow forgot to do this before. Storing teh use count with
the object saves some cpu cycles, and avoids some memory fragmentation.
Thread-safe truth values

Turns out I was naive about just how thread-safe shared pointers are.
The documentation said that "shared pointers are as thread safe as
raw pointers". Actually, they are less thread safe than raw pointers.
Raw pointers are at least atomic, shared pointers are not even that.
Arghhhh.
Misc cleanup from previous changes.

The high(er)-performance API for truth values won't take version
handles.  Switch the code over to use the new API.
Update PLN example for #507
Update PLN README
Update PLN README