* Alphabetized third-party DB backend list.
* Added backticks around single-word link texts to ease visual/machine sorting.
* Added CockroachDB to list of third-party DB backends.
* Updated third-party DB backend URLs.
Thanks to Nick Pope and Tim Graham for the review.
Backport of 6dcfa70cac29c854fc5169bed1cf6479eabdb8c1 from master