LINKing to documents and Diff/Changelog autoescaping fix

This release includes a new feature, a bug fix, and some documentation updates.

• The [LINK: ...] feature now supports linking to documents by UID. [@haxtibal]
• HTML escaping was fixed on the Diff/Changelog screen. [@haxtibal]

The documentation now includes two new pages:

• The "Feature Map" document provides a high-level overview of the major StrictDoc features from the user's perspective.
• The Troubleshooting document offers advice on clearing the user cache, one of the common solutions to user issues. We plan to expand this section with more tips over time.

What's Changed

• Bump version to 0.2.0 by @stanislaw in #1984
• Regenerate CHANGELOG by @stanislaw in #1985
• docs: migrate several links to new @relation syntax by @stanislaw in #1986
• Track UID_TO_NODE for SDocDocument to resolve LINK to DOCUMENT by @haxtibal in #1987
• docs: caching, troubleshooting, roadmap by @stanislaw in #1989
• Update issue templates by @stanislaw in #1990
• .github: add/edit the issue templates by @stanislaw in #1991
• .github: bug_report: use the same markup as for the feature by @stanislaw in #1992
• docs: user guide: enable MID by @stanislaw in #1995
• diff/changelog: remove an outdated MID component by @stanislaw in #1994
• docs: enable MID for all remaining documents by @stanislaw in #1996
• Mark diff colors safe and escape raw diff input by @haxtibal in #1993
• docs: feature map by @stanislaw in #1997
• Code climate: Diff screen view objects: remove unused code by @stanislaw in #1998

Full Changelog: 0.2.0...0.2.1