Improve and possibly vendor-in the tabulate package to get required functionality

[andy-maier]

pywbemtools is using the tabulate package. We have proposed improvements for the nested table support it only very partially has right now, including a PR ready to be merged, but the maintainer of the package seems to be gone.

We need nested table support in order to address issue #249. See there for details on tabulate and the proposed change.

This issue is to fork the tabulate repo, so that the changes we need can be done there, and to include it as a vendored package within the pywbemtools package.

[andy-maier]

Before we start forking tabulate (from its current repo on GitHub https://github.com/astanin/python-tabulate), we should work out what the issues are that we see, and whether we can deal with them.

[KSchopmeyer]

Moved to v 0.9.0 and also moves issue #249

[andy-maier]

Wanting for narrowing down the option space in issue #249 so we understand what the issues are that need to be addressed in tabulate.