DNM: NITX Feature#47

Draft

vertose wants to merge 4 commits intomwcproject:masterfrom

Commits on May 3, 2022

defining transaction models
vertose
committed

Commits on May 24, 2022

migrate output positions to id-based keys
vertose
committed

Commits on May 27, 2022

migrate spent commitments to ids and finish moving all input and output handling to id-based (sans APIs and a few tests)
vertose
committed

Commits on Jun 24, 2022

libtx builder for non-interactive txns
vertose
committed