G1: Add a G1 syntax for parsing

G1: Add a G1 syntax for parsing

This is based on the generic_at parser, with unnecessary stuff removed.

The G1 routinely screws up CRLFs, so the parser needs to account for
that.  This parser ignores leading CRLFs (which is what reference-ril
does as well), as well as trailing LFs (which are sometimes left out).
CRs are used as end-of-message indicators.  Since we're not bothering
tracking CRLFs, there's also no need for a GARBAGE state, or MULTILINE
stuff.