In Python 3, the default encoding of source files is utf-8. The encoding
cookie is now unnecessary and redundant so remove it. For more details,
see the docs:
https://docs.python.org/3/howto/unicode.html#the-string-type
> The default encoding for Python source code is UTF-8, so you can
> simply include a Unicode character in a string literal ...
Includes a fix for the flake8 header checks to stop expecting an
encoding cookie.
* rename a few test modules to make the names more consistent
* do not copy/use Sphinx from build/ (unnecessary without 2to3)
* use a temporary dir for *all* test projects, the source tree
will stay pristine that way (default is tests/build)
* speed up tests by ~3x by splitting up test projects and avoiding
rebuilds
