Use reference links in Markdown.

[jaydenseric]

This can dramatically reduces the volume of markdown. Fixes #948.

This approach might be problematic when inserting markdown under a readme heading if the readme already has link references with conflicting IDs.

One option might be to use a customizable prefix for the numeric link IDs to act as a namespace. Perhaps using the insertion heading string by default?

For the record, I did try remark-defsplit but chose not to use it:

• It does not consolidate link references at the end of the markdown, but at the end of the first section in which they are used. This seemed fragmented and messy.
• Although the string references are more readable, they are longer than using numbers.
• If we solve the namespacing issue with a prefix, the string id's will be confusing since they are meant to display the subdomains and domain of the link URL.

What seems like a good idea for an alternative, is a Remark plugin that creates references based on short hashes of the URI being referenced. That way, you only need to worry that the bookmark IDs being linked are document-unique, which is something that needs to happen regardless.

[tmcw]

Merged in #1031 which fixes tests & disables this in readme mode. Thanks!