revlog: split the `version` attribute into its two components The `revlog.version` attribute contained an integer coding 2 different informations: * the revlog version number * a bit field defining some specific feature of the revlog We now explicitly store the two components independently. This avoid exposing the implementation details all around the code and prepare for future revlog version that would encode the information in a different way. In the process we drop the `version` attribute from the interface. It was flagged for removal when that interface was created. Differential Revision: https://phab.mercurial-scm.org/D10565