Memoization support
Memoization support

Adding a memoization_lookup_table that uses a hash of inputs at task launch,
and stores the result/futures. Duplicate tasks can be avoided if a lookup
hits at launch time. Tested. Passing flake8.

swift-lang/swift-e-lab,Parsl/parsl,Parsl/parsl,Parsl/parsl,Parsl/parsl,swift-lang/swift-e-lab