Supersedes inikulin#397

Previously, `ctLoc` was overwritten on every new character. inikulin#397 attempted to improve this by maintaining the locations in an updated object, and creating copies when needed.

With this PR, we instead use explicit offsets when creating tokens. There is no more need to update locations; instead, we exploit the fact that a *DATA state is entered only after emitting the previous token.

This change should lead to a great reduction in allocations when using location information.

Merge `ctLoc` and `currentAttrLocation` as `currentLocation`