2.0.0

CHANGES:

Generalize the type of locations to offer more flexibility.

As before, a location corresponds to a pair of begin-end positions.
However, positions are now abstract. A position can be created as
before from a Lexing.position. Alternatively, a position can be created
from a (line,column) pair, or directly from an offset in the file,
or by shifting an existing position by a given offset.

(contributed by Simon Cruanes)