Rebase on upstream 0.6.0

[real-or-random]

A special difficulty is the musig module. I suggest:

• One PR/script run for everything before the upstream musig PR.
• One PR/script run just for the upstream musig PR. We need to solve the conflict manually, but that's easy: simply remove our directory and our changes and prefer upstream.
• One PR/script run for everything after the upstream musig PR.

[Mstone87]

A special difficulty is the musig module. I suggest:

• One PR/script run for everything before the upstream musig PR.[ ] One PR/script run just for the upstream musig PR. We need to solve the conflict manually, but that's easy: simply remove our directory and our changes and prefer upstream.[ ] One PR/script run for everything after the upstream musig PR.

Musig

[Mstone87]

Musig

[Mstone87]

Musig