Add preliminary bus README
Add first draft I2C bus

This is largely a brain dump / code dump, totally untested
Default raiseonerror when debugging
Add argument option to periph thread
Add handshake to I2C bus startup
Add C I2C bus. Again, largely code dump, untested, unintegrated
Can't overwrite stack constant
Actually create an i2c instance
Fix some pretty print issues
Hook up send logic
Fix unpacking, add some logging
Fixup hostname creation from client
Remove debug_

It was a cute idea, but it doesn't allow DBG1 & co to be used
in constructors (as they precede argument parsing). No method
is obvious that doesn't yeild inconsistency between those two
program aspects.
Add missing signal to wake sender thread
Basic dropped client support

Will need rework if there are multiple clients as any client
dropping mid-transaction will destroy the whole transaction
in the current form.
Switch connect failure to a trap to allow retry
Debug / Output prettifications
Fix m3_ctl::i2c_write parsing, conflated write's
Add bus ACK support
Fixup simple.bin to do intelligent things