Remove unused Docjson module.
Less 'open Cow'.
No 'open Hashtbl'; whitespace.
Pull out common components of output_X_file functions.
Rename fold_html ~> concat_html.
Narrow the Html_utils interface.
Remove some unused functions.
Remove labeled argument, since it confuses the syntax extension.
Split out an 'Html' module, with the basic operations on HTML.
Combine "insert_between" and "concat" into a single function with an optional separator.
Make (most) globals writeable only from a single module.