PSSA 1.21.0 docs changes from PSSA repo (#99)

* PSSA 1.21.0 docs changes from PSSA repo

* Revert changes with absolute to relative link as those links are different between PSSA vs MicrosoftDocs

* Update reference/docs-conceptual/PSScriptAnalyzer/Rules/AvoidSemicolonsAsLineTerminators.md

* Update version in TOC

* Update with changes from PowerShell/PSScriptAnalyzer#1844

* Update AvoidUsingPositionalParameters docs from last PR

Co-authored-by: Sean Wheeler <sean.wheeler@microsoft.com>

Author: bergmeister