WIP: Roadmap for script analyzer

[JamesWTruher]

I'm working on a long-range plan for PSSA, but here are some things which I think are needed:

• Move to Pester 4: Changes to allow tests to be run outside of CI #882 and Update from Pester 4.1.1 to 4.3.1 and use new -BeTrue and -BeFalse operators #906
• Make sure that tests are runnable from repo
• Run CI on Mac/Linux
• Improve automation for release
• Reorganize repository (group rules, only rules in rules folder)
• Improve consistency with other PowerShell repos (build/test scripts, etc)

[joeyaiello]

Probably need to revisit the CONTRIBUTING.md and repo documentation as well.

[bergmeister]

Would it make sense to have a base repo for basic CI helper stuff and contributing guides? Most repos could then use this common repo as a submodule. I know, submodules can be bad but if the foundation is solid then this would be a way of unifying the processes across repos.

[bergmeister]

Any thoughts on the following points?

• AppVeyor does not work in forks due to non-public WMF4 image
• Branching: development happens in development branch instead of master
• Running tests against/using PowerShell Core in CI