Design notes added

["Beckerle, Mike" <mb...@tresys.com>]

I added 3 new design notes about the Daffodil schema compiler space/speed issue.

You can the design notes on the daffodil site, where an area for developer-centric documentation<https://daffodil.apache.org/dev/> has been created.

These are on the daffodil web site because I created them using asciidoc, which has some big advantages over wiki-based developer doc, and you can see the features it provides at the aboutAsciidoc page<https://daffodil.apache.org/dev/aboutAsciiDoc/>.

The 3 pages are under: https://daffodil.apache.org/dev/design-notes/

  *   term-sharing-in-the-schema-compiler
  *   hidden-groups
  *   namespace-binding-minimization

That makes them easy to read, as it formats them, renders the diagrams, etc.

The beauty of asciidoc is that it is also reviewable using code-style code-review tools as available on github for source code review.

A PR which includes the asciidoc files is https://github.com/apache/incubator-daffodil-site/pull/18

This PR has already been merged (or you wouldn't see the rendered html pages on the daffodil-site), but comments made there still come through as notifications to developers.

This review workflow is still subject to change. I don't like the notion that people are reviewing via a closed PR.