Formatting upgrades

[lsorber]

• Autopep8 formatting.
• Flake8 valid with --max-complexity=10.
• isort formatting.
• Improved logging: logging.INFO by default + better formatting + fixed small logging bug.
• Fix two bugs in get_hash: (1) task graph constants may in fact be dependencies instead of arguments, in which case they should be added to the dephash_list, (2) undid adding of dependency hashes to the arghash_list in order to make interpreting hash misses easier to reason about (args=literals, deps=dependencies).
• Simplified interface: graphchain.optimize and graphchain.get.

This is what the new logging output looks like:

import graphchain, logging
logging.getLogger("graphchain").setLevel(logging.DEBUG)

dsk = {'a':1, 'b': 'a', 'c': 'b'}
graphchain.get(dsk, 'c')

# 2018-05-31 23:44:03,523 graphchain INFO Initializing cache
# 2018-05-31 23:44:03,523 graphchain INFO Initializing graphchain.json
# 2018-05-31 23:44:03,524 graphchain DEBUG CACHE MISS for key=a with src=NONE arg=NONE dep=NONE (0 candidates)
# 2018-05-31 23:44:03,525 graphchain DEBUG CACHE MISS for key=b with src= HIT arg=MISS dep=MISS (1 candidates)
# 2018-05-31 23:44:03,525 graphchain DEBUG CACHE MISS for key=c with src= HIT arg= HIT dep=MISS (1 candidates)
# 2018-05-31 23:44:03,525 graphchain DEBUG CACHE MISS for key=c with src= HIT arg=MISS dep=MISS (1 candidates)
# 2018-05-31 23:44:03,526 graphchain INFO EXECUTE + STORE key=c literal=<class 'str'>
# 'b'

graphchain.get(dsk, 'c')
# 2018-05-31 23:45:14,825 graphchain DEBUG CACHE MISS for key=a with src= HIT arg=MISS dep=MISS (1 candidates)
# 2018-05-31 23:45:14,826 graphchain DEBUG CACHE MISS for key=b with src= HIT arg= HIT dep=MISS (1 candidates)
# 2018-05-31 23:45:14,826 graphchain DEBUG CACHE MISS for key=b with src= HIT arg=MISS dep=MISS (1 candidates)
# 2018-05-31 23:45:14,826 graphchain INFO LOAD key=c literal=<class 'str'>
# 'b'

(Note that the output in the above examples is incorrect because of #16. The point is to show the logging output.)

[lsorber]

@zgornel Most of the diffs are due to the autoformatting. I'm aware this makes reviewing harder, sorry about that :$. But check out the changelog and look for those changes, we can discuss the rest together!

[zgornel]

Looks good, nothing to add ;)