Description of problem:
The "publican create" action generates an entities file for new books with some commonly useful entities pre-loaded into it.
However, extra entities might be useful to a brand -- for example, a project might want to specify an entity that contains a URL to their bug tracker. Brands can already call new entities in their Common Content files, but without a corresponding entity in the .ent files of newly created books, these books will not build.
Brands might also want to provide defaults or overrides for the standard Publican-supplied entities; in particular, for the &HOLDER; entity, which is typically the same right across a project.
Version-Release number of selected component (if applicable):
Long stated policy is that we will not expand entity support in any way and we will kill it off if we get half a chance ... DocBook5 is at least a 45% chance.