Replace parse_inlines_while with parse_inlines_from_subject.
Removed config.h.cmake (not used).
Factored out push_delimiter.

Conflicts:
	src/inlines.c
Removed unused emphasis_nestlevel.
Improved fuzztest.
Improved fuzztest.
Spec:  better system for designating definitions of terms.

`[foo](@foo)` turns into an anchor with id `foo` that links to
itself and has class `definition`.  This allows us to remove the
manual `<a>` tags in `spec.txt`.

A simple regex substitution in the Makefile handles the transformation.

I believe this addresses some of the concerns in #141 by giving
the definitions a prominent appearance.  Note that
we want definitions to link to themselves, to allow users to
quickly generate a link to the relevant bit of the spec.
Make spaces visible using CSS.

Closes #49.

I didn't want to actually insert the characters, since I want
the code samples to be cut/pasteable.  But this CSS trick seems
to work.
template.html changes needed to make visible spaces work.
Simplified link_label parser.

It now just scans for an unescaped `]`.  No `[` characters are
permitted in labels.  Backticks don't have their usual meaning in
labels.

This accords with the behavior of some of the main Markdown parsers:
marked, sundown, discount, kramdown, showdown, Markdown.pl,
PHP Markdown.
Initial steps towards link parsing.
Got inline links working.
Got ref links working, but with deallocation issues.
Fixed allocation issue.
Fixed problem with images.
Fixed backslash-escape inside link label.

Down to 8 failures, all cases where the spec will need to be
changed to reflect lack of priority of links over emphasis.
Disallow links inside links and images inside images.
Removed some unused code.
Added MAX_LINK_LABEL_LENGTH to cmark.h.

Use in link label parsing and reference lookup.
runtests.pl:  distinguish error status from failures.