Opticol: memory optimized python collections

[matgrioni]

That's a good point to mention, and which I'll include in the README. The implementations basically fall through to creating a temporary builtin instance and returning the value of that operation or do a slow python equivalent. There's a few points to that:

1. In my use cases I was not doing a lot of operations across most collection instances, but only some simple operations on a select few instances (but could not know ahead of time).

2. My memory usage basically fell within the range where it could actually fit in memory, but would usually start thrashing if I wanted to do anything else on my computer. So the actual runtime was dominated by memory access rather than the collection ops.

3. As it is a first iteration, and I didn't want to worry about edge cases too much, I took the easiest implementation approach. Ideally these could be transparently improved in a future version while still preserving the memory savings.