Split out CFob grammar from other round-tripping

[orcmid]

The obstring.txt is perfect for mindelay output of obs in canonical form.

1. Change that to CFob.txt or CFstring.txt as considered most appropriate.

2. Make a version that is sugared to have pure-lindy constructions be like text. Maybe it is a CFtext. It still reduces to a CF and it outputs again as a CFtext. This is more likely for oFrugal.

3. The only problem is maybe this creates a conflict with more-extensive versions of Frugal.

This is discussed at #65