Module "clock/xd" Port Naming

[WillGreen]

The lib/clock/xd.sv module has ports named _i and _o. The port names suggest signals are inputs and outputs even when they're not. Source and destination based naming would be clearer.

Changing the module is straightforward, but its used quite widely, so a fair bit of testing will be required.

[WillGreen]

There's a new module temporarily named xd2. Once it's rolled out everywhere, we can replace the original xd.

[WillGreen]

This was fixed by PR #129 in November 2022. The blog was updated in October 2022: https://projectf.io/posts/lib-clock-xd/