use cmake and python to keep version numbers updated

[arezaii]

This uses a combination of python scripts and cmake dependencies to keep the version number information consistent with the information in CMakeLists.txt. The purpose is to avoid manually having to update the version number across a variety of documents with every release. With this change, the version numbers will be correctly updated based on the status of the CHPL_OFFICIAL_RELEASE flag, and the current, previous, and next version numbers.

This necessitated tracking the next and past version numbers as the versionButton.php file needs the next version number when the CHPL_OFFICIAL_RELEASE flag becomes true, and at the same time the archived-spec.rst file needs to know the previous version number.

Because we can't predict the past or next version number from the current one, it was necessary to add these to the CMakeLists.txt file.

New files that need updating can be handled by creating new instances of the FileUpdater class and implementing the update method.