Doxygen.
Intorduces C-level API reference generation with Doxygen.
* tool/file2lastrev.rb: wrapper script that abstracts subversion
and git-svn.
* tool/strip-rdoc.rb: filter for preventing doxygen from processing
rdoc comments.
* configure.in: (Doxyfile): Doxyfile is generated together with
Makefile.
(PACKAGE): configuration $(PACKAGE) is necessary for $(docdir).
* instruby.rb: adds a new install target 'capi'
* common.mk (capi): new target that generates C API documents with
Doxygen.
(install-capi): new target.
(pre-install-capi): ditto.
(do-install-capi): ditto.
(post-install-capi): ditto.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@20919 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
