[osis-core] header info format again

[Harry Plantinga]

I am still forced to drop header info in the OSIS header.
I have author names in two forms: "short form" and "file-as",
e.g. Alexander Whyte and Whyte, Alexander (1836-1921). I
don't have any good way to include both forms, since the type
attribute has other uses:

  <creator type="Author">
  <creator type="Editor">

etc.

If it were possible, I'd like to be able to say

  <creator type="Author" format="short-form">Alexander Whyte</creator>
  <creator type="Author" format="file-as">Whyte, Alexander
(1836-1921)</creator.

I realize I might be able to do that by including a TEI header, but
that seems rather to be overkill...

-Harry