Memory leaks

[ul]

When using pararules in my project, I noticed two kinds of memory leaks:

• Cows leak memory on each fireRules.
• Independent of that, it seems that retracting facts doesn't decrease the network's memory consumption, and the network grows relatively big for a modest number of rules and facts.

I'll fix the first as I introduced the cow solution, but I'm unsure what to do with the second.

[ul]

Actually, I struggle to find why CowTable is leaking memory =(

[oakes]

Hmm yeah I can definitely see the leak. How about I revert for now and you submit a new PR if/when you find the leak?

[ul]

Solved with switching to the ptr and manual memory management.

This leaves us with garbage collection for the network itself. It grows when I add facts but never shrinks, independent of using CowTable or Table.

[oakes]

Still leaking for me but I'll make a new release with the revert and we can take our time finding a fix. It's all good -- neither of us noticed :D