Yet more SCons build.

- Also copy CSS for "quick Charms HTML".  And we don't need an explicit dependency
on the per-Charm-tree PNGs, because we depend on the per-Charm-tree HTML, and
that itself depends on the PNGs.
- Change the "image-dir" attribute for the AsciiDoc call to match the location under SCons
(as opposed to the location when I was using the Makefile).
- Switch most uses of Depends to Requires.  For HTML-building we don't need to re-generate
the HTML just because there's a change in something it includes or links to.
SCons: Add in dependencies on Ruby scripts and for each of those, on yaml2x.rb.
SCons: Remove a bunch of commented-out stuff that I'm sure I don't need to refer to any more.
SCons: Remove more commented-out stuff.
SCons: Factor out the YAML-based builders for brevity.

Also, delete some more commented-out stuff.