(GH-316) Fix KAC violations in CHANGELOG
(GH-316) Fix KAC violations in CHANGELOG

Prior to this commit the project inconsistently applied
the [keepachangelog](https://keepachangelog.com) standard.

This commit makes several fixes to the file:

- It ensures released versions are wrapped in square
  brackets.
- It ensures every release includes appropriate sub-
  headings.
- It removes non-user facing information to reduce
  the cognitive load on readers.
- It rewords some of the messages to be more clear
  and user facing, as well as converting them to be
  sentences.

This resolves #316.

jpogran/puppet-vscode,glennsarti/puppet-vscode,jpogran/puppet-vscode