make doc xrefs link to section headers
add versioning notes to features in the manual

This helps guide which ninja version to depend on.
manual: move in_newline to the reference

It's a detail, it doesn't belong in the brief tutorial overview.
Removed unused UnitsWaiting() function from State class.

This function was added at 307f0bbd("and some basic implementation"), but nobody
calls it anymore.

Signed-off-by: Thiago Farina <tfarina@chromium.org>
Fix wrong usage of std::string::find
Merge pull request #506 from syntheticpp/string-find

Fix wrong usage of std::string::find
Browse command does not parse URL correctly
Merge pull request #502 from tfarina/rm-unused-fun

Removed unused UnitsWaiting() function from State class.
Merge pull request #507 from ikarienator/master

Browse command does not parse URL correctly