Quickbook: doc info improvements.

- Fix handling empty category attributes.
- Quickbook 1.6: Scope source mode changes to the file they're made in.
Quickbook: merge 'values' from quickbook-filenames branch.
Richer copyright syntax.
Quickbook: fix simple markup.
Quickbook: merge further 'value' development.
Quickbook: Tweak doc info for empty attributes.

Maybe these should fail.
Quickbook: A couple of hidden flags for testing.
Quickbook: simplify a couple of things.
Quickbook: nestable elements. Refs #1193
Quickbook: note about nestable elements.
Quickbook: Go back to using invalid markup for lists.
Quickbook: clean up the value stuff.
Quickbook: some fixes for Visual C++.
Quickbook: Implement int value and use for years and versions.

Hopefully will no longer need to the workaround for 64 bit gcc.
Quickbook: further improvements for simple markup.
Quickbook: store a copy of the string in utf8_proxy.
Quickbook: support escapes in simple markup.
Quickbook: more use of phoenix.
Quickbook: better anchor placement for lists.
Quickbook: pass-thru comments.