cleanups and omd support

+ whitespace cleanup
+ merlin support
+ simplistic support for markdown parsing via `omd`

the latter is probably rather inefficient and potentially brittle and certainly dumb as it simply uses `omd` to parse markdown to an HTML string; and then uses `cow`'s existing HTML parser to parse to `Cow.Html.t` to then integrate with `cowabloga` which then does various templating and styling things with that representation.

assumes `omd.0.8.1` -- current version in stable opam repo appears to be 0.6.0.