Merge pull request #116 from tpkelly/develop

Introduce groupKeyFunction
Update README.md

Update NPM link
Renamed tickRotation to tickLabelRotation.
Renamed labelFormat to tickLabelFormat.
Renamed tickOrientation to tickLabelOrientation.
Update README.md
Reverted change to tickLabelRotation in README.
Added missing JsDoc comments.
Updated changelog.
Fixed copy/paste error.
Merge pull request #117 from niksoper/master

Renamed Axis tickRotation and labelFormat
Merge branch 'upstream' into develop