Glasgow Embedded / Glasgow - History

gateware.pll: adjust for nMigen.

This doesn't include adjustments for gateware.platform. Fortunately,
only a few applets use PLL, so this can be done later.

gateware.pads: adjust for nMigen.

nMigen provides a native replacement for what Pads was trying to do,
so this module is essentially deprecated, and no particular care has
been taken to keep it in good shape.

gateware.analyzer: adjust for nMigen.

There were three issues:
* nMigen SyncFIFOBuffered no longer provides access to the inner
FIFO. Therefore, level of the outer FIFO is used instead.
* nMigen simulator no longer allows setting Signals that are not
actually used anywhere in simulation.
* In nMigen, FIFOInterface.read() is 1-cycle, not 2-cycle.
This requires adjustment of our read loop (which would ideally
be rewritten.)

Bulk port of all gateware to nMigen compatibility layer.

cli: make FILENAME argument of run-prebuilt optional.

Most of the time you're just copying around the output of build,
which already has a default filename.

cli: flush and cancel demultiplexer after running applet.