[pcb] clarify pin functions
[pcb] re-assign sensor interrupt pins
[pcb] increase C5 size from 0603 to 0805
[pcb] correct HTU21D footprint
[pcb] rename passives
[pcb] update board layout
[pcb] use smaller + round pads for I2C header
[flt] add pull-up to ISP_EN pin
[flr] update RFM69 silkscreen
[flr] add ptc fuse in series with battery
[flr] improve pcb routing