Add a custom GB ROM for a better interface than GBlinkdl

[Vicki Pfau]

GBlinkdl has several problems:

• It dumps bank 0 always
• You cannot establish a new connection or figure out if you already have an open connection; you need to restart
• It doesn't support batch writes (afaik)

etc etc etc

It would be good to fork or rewrite it to be more convenient.

[Vicki Pfau]

See https://github.com/endrift/gblink2