[osis-core] Is this ready for OSIS 1.1? Header

[Todd Tillinghast]

Did we address Harry's concerns regarding the header?

I continue to find the header to be limiting.  It seems that any useful
header will be a part of future release.  Should we consider splitting the
header into its own schema (OSISHeader for example) and then include which
ever header is most suitable in the non-abstract schema used.  (Of course
this implies that OSISCore is abstract.)

Shouldn't teiHeader be TEIHeader?

Todd