py.test and moving tests out of lib path

[grigi]

Done:

• Pulled the py.test changes from [WIP] New pooling for mysql and asynpg #141
• Moved tests out of the library path.
• Moved the of the dev-oriented requirements out to the tests folder.
• Collapsed Travis/tox runs to do full test suite for each supported language
• Do backup tests via green instead of py.test
• Moved extra_requirements.txt to tests/
• make ci now runs tests against ALL supported DB's
• made py.test runs multi-process for a significant speedup (still slower than green, though)

This should do a few things:

• Less CI runs on Travis should let it complete faster.
• Cleaned up the root folder
• Tests no longer in the library module path, so a little easier to keep separate.
• Since coveralls broke in handling multiple test runs, at least now the coverage reported will be correct.
• Default to py.test due to a bit more features (e.g. collect warnings, etc) Although performance is notably slower than green, it is still worth it for the extra flexibility.

[coveralls]

Pull Request Test Coverage Report for Build 787

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+2.4%) to 98.101%

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Totals
Change from base Build 774:	2.4%
Covered Lines:	5704
Relevant Lines:	5768

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💛 - Coveralls

[grigi]

@abondar Please review. I took the relevant changes from your PR #141