Formatting of POD & code.

Merging, with adaptions, of patch from Andy Yates:

  Changes to regular expressions for detecting multi-species databases,
  including multi-species compara and ancestral databases.

  Added method find_and_add_aliases() which in the future may be used to
  read species name aliases directly from the meta tables rather than
  having the species aliases hard-coded in this module.

Tested with multi-species databases as well as with native Core
databases.