nmigen project name changed to amaranth.

[lethalbit]

This is more of a heads up than an issue, but the nMigen project has officially been rebranded amaranth-lang (new home is at amaranth-lang), and as such that would need to be updated here.

The core amaranth package and the -boards package have a thin compat layer but the -soc and -stdio packages do not.

Also there are some things which the Luna gateware uses that are not included in the compat layer, such as the nmigen._unused module so that import breaks.

All things considered it should be a fairly simple forward port, so this is just a heads-up to the change

[straithe]

Thank you for this update! We appreciate the heads up.