Add allocation hoist optimization

[arshajii]

No description provided.

[marioroy]

The alloc-hoist-opt branch core-dumps running the murphy.py demonstration (tested without memorization).

# Codon 0.16.3
codon build -release murphy.py
time ./murphy
5.797

real  1m29.675s
user  4m44.102s
sys   0m35.530s

# Codon develop branch
codon build -release murphy.py
time ./murphy
5.797

real  0m49.610s
user  3m15.357s
sys   0m19.421s

# Codon alloc-hoist-opt branch
codon build -release murphy.py
time ./murphy
AssertionError: Assert failed (/tmp/murphy.py:104)

Raised from: play:0
/tmp/murphy.py:104:5
Aborted (core dumped)

real  0m0.411s
user  0m0.180s
sys   0m0.198s

Linue 104 is assert len(scenarios) == 1.

[arshajii]

Thanks @marioroy -- I've fixed this. Also it seems like the linked issue is resolved, as on my machine the timings are now 40s for Python and 27s for Codon (haven't done a detailed benchmark though).