Add configuration for coverage measurement
Merge pull request #185 from ayust/coverage

Add configuration for coverage measurement.

This publishes coverage statistics from the Python 2.7 build to https://coveralls.io/r/eve-val/evelink - the reason Python 2.7 was chosen is that it is the build which includes AppEngine tests.
allow newer version of requests

It appears that the requests library had some python3 compatibility issues that
were fixed between version 1.1.0 and the current version.
Add coverage badge to README.md
actually set the minimum version
bump requests requirement to latest version
roll back to a more conservative minimum version
Merge pull request #186 from stesla/python3-compat

Move to using requests 2.0.0 or higher.