tests: ship tests in source distribution

Including tests allow people interested in running tests for a given
release to be able to do so without checking out git.
docs: include documentation in source distribution

Useful for distributions wanting to ship documentation with the
cookiecutter package.
Merge branch 'fix/include-doc-tests' of git://github.com/vincentbernat/cookiecutter into vincentbernat-fix/include-doc-tests
Merge branch 'master' of github.com:audreyr/cookiecutter