Implement a symbolic collections.deque

[pschanely]

Per #2, deque cannot be analyzed symbolically. Tentative plan is to implement a "dumb" version on top of a generic list:

CrossHair/crosshair/simplestructs.py

Line 57 in 56ce14e

# TODO: implement collections.deque on top of SmtList:

[oneEdoubleD]

I'll take a look at this once you've finished refactoring the implementation pattern

[pschanely]

Thank you for taking a look! I've given the basic framework for how I imagined it here:

7a4e460

But use your best judgement too, and feel free to be noisy in the chat while you investigate!

[pschanely]

Just a note for later: pypy actually also has a pure python implementation of this: https://bitbucket.org/pypy/pypy/src/default/lib_pypy/_collections.py

[pschanely]

I think 7df7f86 ties up the last loose ends for this one!