add diode in reset line from Ser+

[tht]

Looks like it's working perfectly fine but there should be a diode in the reset line to make sure the BP is always able to do a clean reset.

[jcw]

To clarify, although maybe it does not apply exactly to F103: on L052, a diode was needed to make reset 5V-tolerant and to support software reset, which causes the reset pin to be pulled low internally and act as an open-collector output. When tied to a stiff "1" logic level, software reset will fail.