BREAKING CHANGE: Generate UnitSystem default abbreviations

Not backwards compatible with custom units API.
Make methods public instead for manually adding abbreviations, same
methods used to seed default abbreviations.
Convert unit class templating to powershell here-string

And move functions to external files to be included
Convert unit enum template to here-string
Remove obsolete files
Rename include script files to have prefix "Include-"
Move unit definition files to separate folder
Add support for xml doc on unit enums
Add mass units
Fix bug in generated static From methods
Add pressure unit
Generate all units up until now
Add ratio unit
Add unit rotational speed
Add unit Speed
Rename files to camel case
Add unit Temperature
Add unit torque
Fix tab to space
Fix tab to space
Add unit volume