Incorporate CHANGELOG into documentation.
Correct MANIFEST.in.

It was missing requirements.pip and had the wrong README file.
Make setup.py executable.
Move version management into module.

Previously the version was manually entered in both the setup.py and
the documentation configuration.  This commit switches it to use the
community standard `__version__` and `version_info` attributes at
the top level of the package.
Bump version to 1.5.2.
Merge pull request #8 from aweber/release/1.5.2

Release 1.5.2