Write our debug logging module

[dhylands]

Ideally, I'd like this to work like printk does in the linux kernel. printk can be called from ISR code or from task code and it does things so that the latency between printk's called from the ISR level and when the data shows up on the serial port is minimized. This makes the output a bit more synchronous, but makes it MUCH more useful from a debugging standpoint.