pyVmomi reStructured Text Documentation

This external documentation for pyVmomi was generated using Googly Docs
(aka Google Standard Documentation) which renders very cleanly in
GitHub. Internal documentation for a class should be done in Sphinx
format because tools like pyCharm and Eclipse can use that documentation
as a hint for code completion.

Note: External docs as Googly Docs, internal docs as Sphinx.

Closes https://github.com/vmware/pyvmomi/issues/15