Adding cons function and heap class (marking implemented but not yet free)
Updating README.md
Adding basic working (I think) garbage collector built out of cons
Adding support for GC of lists. Todo: Code review on approach
Fixing eval for sequences, so that [[1,2],3,4] evals to the expected [[1,2],3,4] native list
Properly supporting list nesting in cons (see README.md changes and new sample file)
Cleaning up GC; only GC'ing lists that were assigned to vars that get assigned to other vars for now; not sure what other scenarios exist
Adding support for list concatenation via || operator
Merge branch 'GarbageCollection'

Conflicts:
	README.md
	programext.py
	test/SampleInputs/cons.p
Changed __repr__ of List to print out a non-memory dependent string