Added documentation for GroupSequence
fixed attribute name
Merge pull request #2647 from ClementGautier/2.0

[WIP] Added documentation for GroupSequence
[#2647] Minor tweaks to new validation group sequence docs
Merge pull request #2660 from bamarni/patch-9

fixed attribute name
Minor fixes to contributing code docs
Align parameters in comment and add array type
Remove oxford comma per request
[#2480] Language tweak per @pvolok
Merge pull request #2665 from jbafford/contributing-code-edits

Minor fixes to contributing code docs
Merge branch '2.0' into 2.1
Merge branch '2.1' into 2.2