Set Date of 1.18.0 release in Changelog (PowerShell#1180)

* Set Date of 1.18.0 release in Changelog

* Add PR 1179 to changelog as well

Merge pull request PowerShell#1018 from PowerShell/development

Merge changes of 1.17.1 (including 1.17.0) into Master

Update PossibleIncorrectComparisonWithNull.md (PowerShell#733)

* Update PossibleIncorrectComparisonWithNull.md

This is technically more accurate. PowerShell doesn't check for a $null in the array as was previously indicated.

* Update PossibleIncorrectComparisonWithNull.md

Revised description based on comments.

Merge pull request PowerShell#813 from PowerShell/v1.16.0

Prepare release v1.16.0

Merge pull request PowerShell#813 from PowerShell/v1.16.0

Prepare release v1.16.0

Merge pull request PowerShell#792 from PowerShell/kapilmb/v1.15.0

Prepare release v1.15.0

Prepare release v1.14.1 (PowerShell#778)

Merge pull request PowerShell#773 from PowerShell/kapilmb/v1.14.0

Prepare release v1.14.0

Merge pull request PowerShell#763 from PowerShell/kapilmb/v1.13.0

Prepare release v1.13.0

Merge pull request PowerShell#757 from PowerShell/kapilmb/fix-align-a…

…ssignment-rule

Make AlignAssignmentStatement rule available on powershell core