omd_backend.ml: fix: html comments handling in make_paragraphs
omd_main.ml: comments
omd_main.ml: options for toc start and depth
omd_main.ml: comments
omd_main.ml: module now fully documented
omd_parser.ml: comments + replace [split_norev] and [split] by more general [fsplit_norev] and [fsplit]
_oasis: updated to use recently added modules
omd_parser.ml: fixing a bug in [maybe_reference], introduced 2 commits before (17fc8cf31c175e0599623ba47d39143e43203028).
omd_main.ml: removing a useless let-open-in
test.ml: updating it to make it more useful (still needs work)