Add links.yaml for link test fixtures
Add test cases for new link parser
Small reordering of tests
Add glypher for quoted quotes.

Allows handling of quoted quotes such as "The '"' is a funny character".
Useful for preventing problems looking for the start of links when the
link text contains embedded quote characters.
New link parser.

Replaces the old single-pass parse with a two-stage strategy that uses
two new routines: markStartOfLinks() and replaceLinks().
Update changelog.
Add false start-of-link test cases.
Update test case
Randomise $link_start_marker.
Remove dead line of code.
Remove some comments.