As of now, the glossary defined in our documentation reflects the
current state of the codebase. In order to avoid any discrepancy
between the codebase and each definition, the objective here is to
gather both in a single place and link it into the rst documentation
via a custom directive.
Also re-aligned the requirements with liberty for doc.
DocImpact
Change-Id: I9ca50f8d3c32b4690ee240e13dec0cb7eeedcc2c
