make separator configurable through `data-separator`
make separator configurable through `data-separator`

`data-separator` attribute on a wrapped input element can be used to
specify tags separator

We use `KeyboardEvent.key` to detect separator, if browser does not
support it (Safari) we fall back to KeyboardEvent.keyIdentifier

see:
http://caniuse.com/#search=KeyboardEvent.key

code42day/tags-input,code42day/tags-input