Rename delimiter_stack to delimiter

The struct actually describes a delimiter. I also find it conceptually
much clearer to think of a doubly linked list of delimiters than a stack.
Simplify push_delimiter

Always modify the subject when pushing a delimiter.
Simplify remove_delimiter
Eliminate delim_count in struct delimiter

Use literal length instead.
Rename member first_inline to inl_text in struct delimiter
Merge pull request #228 from nwellnhof/delimiters

Rename delimiter identifiers
Renamed cmark_parser_push -> cmark_parser_feed.
cmark.h:  Use C89 comments.
Added blank line in comment.
Updated make_man_page.py to use C89 comments.

See #224.

TODO: change this to create the man page directly (not via markdown
intermediary) and parse signatures into .Ft, .Fo, .Fa, .Fc, .Fd.
Create man 3 page without markdown intermediary.

Use proper man style, marking function types, arguments, etc.

See #224.
Removed markdown intermediary for man 1 page.

See #224.
Set proper name and section in man page.
Man page: proper date format.
Switched to mdoc for cmark.1.
Fixed bug in splitting arguments in make_man_page.py.
Make the man pages standard groff man rather than mdoc.
Fixed commas in man 3 page.
More man page improvements.
Added simple luajit wrapper example.