Remove tests from package but keep them in sdist

1c4727a adds the tests package to the installed packages. This means that when
you install the package you end up with a top level python package called
tests. This is not what we want; this commit fixes this error.

Closes: #139
Add fixtures data to sdist

Whilst the tests dir is included in the sdist package the
tests/functional/fixtures files are not. Fix that.

Closes: #140
Include extra information into sdist package

We should be able to run tests and see licenses etc from sdist.