Update requirements.txt
Add halt method to interpreter
Prune dead phi cycles with no inputs (this breaking type inference)
Merge branch 'builder' of github.com:pykit/pykit into builder
Clean up some types
Merge branch 'master' of https://github.com/filmackay/pykit into vectors

Conflicts:
	pykit/ir/interp.py
Don't import cirparser on import
Add simple bounded cache decorator
Merge branch 'builder' of https://github.com/pykit/pykit into vectors
Fix foreign function as first-class values
Fix argument check for pointer calls
Merge branch 'builder' of https://github.com/pykit/pykit into vectors
Handle representation of recursive types
Formatting, comparing and hashing of recursive types
Merge branch 'builder' of https://github.com/pykit/pykit into vectors
Undef / Null / AllOnes
fake ctypes vectors