DOCS: allow @flipper documentation for feature toggles
DOCS: allow use of @Wikipedia{...} links
DOCS: generate tagfile for reference documentation
DOCS: cross-link tags from "Open Group Base Specifications" and "Single UNIX Specification"
BUILD: add 'download', a recursive rule to download files hosted online
DOCS: move dev build rules into proper Makefile.am
DOCS: copy Rapicorn docs/dev/Makefile.am to Makefile.doxygen
DOCS: use Makefile.doxygen to build documentation
DOCS: remove doxygen enum workaround, not needed with 1.7.6.1
BUILD: add acdoxygen.m4 and depend on doxygen 1.7.6.1
DOCS: Makefile.doxygen: temp dir fixup
DOCS: Makefile.doxygen: use DOXYGEN from configure.in
DOCS: Makefile.doxygen: handle empty/missing DOXYGEN
DOCS: Makefile.doxygen: DOXYGEN_*_GLOBS fixups
DOCS: Makefile.doxygen: prefix remaining variables with DOXYGEN_
DOCS: fixup for CLEANFILES
DOCS: DEV: let docu rebuilds depend on HEAD commit id
DOCS: Makefile.doxygen: fixup for EXAMPLE_PATH
DOCS: update tagfile-susv4.xml
DOCS: remove tagfile-unix.xml, C types are now covered by tagfile-susv4.xml