WIP: Group heirarchy#2

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endgame wants to merge 5 commits intoTaneb:masterfrom

endgame:group-heirarchy

Commits on Nov 6, 2019

Whitespace cleanup
Jack Kelly
committed
Add module header
Jack Kelly
committed
Wrap and reformat haddocks
Jack Kelly
committed
Add RegularSemigroup and InverseSemigroup
Jack Kelly
committed

Commits on Nov 8, 2019

`Group#invert`: move to `RegularSemigroup`, remove `inv`
Jack Kelly
committed