`_type.indices`: rename `Uri` to `Uri-ref`

[vaitkus]

Recent changes in the rc-4.2.0 branch (#32) reverted the definition of the Uri type in _type.contents to mean an 'absolute URI'. However, an equivalent change was not made in the _type.indices attribute definition where Uri is still explicitly defined as an 'URI reference'.

I suggest that we at least rename this enumeration value from Uri to Uri-ref for consistency throughout the dictionary. Not sure if we need to add Uri, Iri and Iri-ref enumeration values.

Pinging @nautolycus and @jamesrhester for opinions since they worked on PR #32.

[jamesrhester]

Thanks for spotting this. I have created #38 and will merge into the RC, which I've alerted the Chester IUCr office about.

[vaitkus]

Issue mostly resolved with PR #38.

However, the _definition.update attribute in _type.indices should also be update to clearly indicate that the definition underwent changes in this development cycle.

[jamesrhester]

Oops! I have corrected the date now.

[vaitkus]

Thanks!