minor bom/dnp tweaks

updated from Si5351C-A to Si5351C-B and added series termination resistor to prevent overshoot from the lower output impedance

visibility fixes for assembly diagram

renamed boot pins to agree with data sheet

switched back to SPIFI boot by default

plot options, zone updates

fixed missing GND on U18

silkscreen zone for writing

updated date on silkscreen

more paste layer improvements