add an API version Provides and Requires

This approach should allow us to make future API changes behave in a
sane way with RPM.  For example, a future imagefactory release can
provide multiple versions of the internal API or eventually stop
providing the original 1.0 implementation.
Merge pull request #306 from aeolusproject/feature/plugin-api-take2

add an API version Provides and Requires
make subpackages own their top level directory
remove spurious unicode character from comments