Markdown Linkify

Replace link shorthands, such as

md In [PS-128], the issue is described in detail.

with actual links. For example, the above could be transformed to:

md In [S-P128](https://www.company.jira.com/issues/PS-128), the issue is described in detail.

Custom replacers exist, so far only for docs.rs and doc.rust-lang.org/.

See test.md for the supported expressions.

Supported link types

Supports [tag]-style "broken links" and many forms of [title or empty](tag "optional hover text").

The specific replacements depend on the matching transformer.

TODO