Release with new Nim 0.19.0 dependency for nil fixes

See release notes. Numeric range checking and nil fixes.

Minor cosmetic updates

Just documentation type changes.

Better Version Handling

See RELEASE_NOTES.md and test/example program Version.nim

Make more NEP1 compliant.

This might just be last release with breaking changes...Famous last words, I suppose. See RELEASE-NOTES.md for details.

Add new mandatoryOverride parameter

No breaking changes.

Make package structure more nimble friendly

All but cligen.nim moved into cligen subdirectory.

Several Breaking Changes & Enhancements

See the new https://github.com/c-blake/cligen/tree/master/RELEASE-NOTES.md file.

version0.9.6

Changed (short|long)Bools in parseopt3 to (short|long)NoArg if anyone was actually using parseopt3 directly instead of through the cligen apparatus.