SM6FBQ / HackRF clone - History

HackRF One: change R60 from 0 ohms to 100 ohms

This matches R31 and was intended to be done when R31 was changed to 100
ohms.

HackRF One: populate R83 instead of R84

This removes clock buffer chaining which was intended to be done when
the RC delay was added.

HackRF One: clean up

- silkscreen
- fabrication attributes
- dates
- copyright
- README

HackRF One: adjust clock phase with RC delay

Remove chaining of buffers to delay GCK2 and instead use an RC delay for
both GCK2 and SGPIO_CLK.

HackRF One: AC couple CLKIN

We've always specified that CLKIN should be DC (based on the Si5351C
documentation), but it has worked with AC input. AC coupling the buffer
input restores this undocumented feature.

HackRF One: chain SGPIO_CLK and GCK2 buffers

This more closely emulates the clock phase relationships on prior
hardware revisions that used the Si5351C.

Update clock trace widths.