Preparing gputils 0.13.7 release

We're planning to release gputils 0.13.7 this week. This release will add
support for nearly all devices supported by MPLAB 8.20 and MPASM 5.30.
(Marko, could you clarify what's still missing? I don't seem to remember.)

We also fixed a few bugs, and I might fix bug #2556391 before then since it
seems trivial.

I can't see there being much else worth trying to include in this release,
but consider this a last call for features to be included in 0.13.7.

David