GitLab

Switched the 'pragma once' to only happen on MSVC, or gcc >= 3.4 (it was causing trouble on the sun compiler)

Flipped the include guard and the pragma, and don't use the pragma for early versions of gcc (< 3.4)

Merged the other-tags branch into the trunk (this wasn't an rX:Y merge, since the branch wasn't branched directly from the head of the trunk)

Moved all the includes to a subfolder yaml-cpp so they don't interfere with other libraries' includes