Run coverage.py with coverage/fullcoverage/encodings.py

[brettcannon]

https://github.com/nedbat/coveragepy/blob/master/coverage/fullcoverage/encodings.py is a hack which makes sure that coverage.py is imported early enough to cover modules that are imported during interpreter startup. Previously it wasn't included with coverage.py, but @nedbat was nice enough to add fullcoverage to coverage.py in https://github.com/nedbat/coveragepy/commit/3962bc4387e4ca69d1e2df280b1021b3db9326fd for its next release. So this issue is to make sure that no one forgets to take advantage of fullcoverage once it's available on PyPI.

[ncoghlan]

Just noting that this will be one of the pre-requisites for even considering disallowing reductions in code coverage (as per #38)

[nedbat]

The fullcoverage file is now packaged, as of coverage.py 4.4b1