Added package hashing logic

[terricain]

Adds logic to calculate package hashes on upload, adds it to file metadata as well so if the database is rebuilt, re-hashing is not needed.

New option pypi.calculate_package_hashes added to control whether to calculate package hashes. Enabled by default as that means the JSON and simple API will act more like the real PyPI.

Depends on #243
Fixes #222

TODO:

• add hashing logic
• test for sha256 url fragment in simple endpoint
• test for hashes in json output
• test for hash calculation on upload
• test for hash retrieval on list
• update docs about pypi.calculate_package_hashes option
• Create Azure and S3 migration script (havent used GCE so someone else can create that when needed)

[coveralls]

Coverage increased (+0.08%) to 82.856% when pulling c2bac33 on terrycain:feature/hashes into 703190d on stevearc:1.1.

[terricain]

@stevearc Ready for a review when you get a chance.

[stevearc]

Looks good! Will cut a 1.1 release by EOW

[terricain]

Awesome thanks