refs #2137

refs #2042 @1h

- Reorganized groups.
- Updated main page.

refs #1996 @30m

- Two documentations may be generated - API documentation
  (Doxyfile) and developer documentation (includes documentation of
  static functions, Doxyfile.devel).
- Developer documentation is generated into the doc-devel/
  directory.

refs #680

- Documentation groups now better reflect modules.
- Fixed documentation markers.
- Fixed ifdef guards.

- Added .o files to .gitignore.
- Renamed parser utility in doxygen main page (knot-zoneparser)