update shell version at each build
events: add function returning number of currently pending events
arch-atmega: add special functions for handling i2c signals (bitbang driver)
mcuio bitbang i2c: make it possible to override scl/sda related functions
mcuio bitbang i2c: don't go to idle while no pending events are there

This speeds up i2c transfers by avoiding useless idle loops (just go
on doing what we're doing until somebody really needs the cpu).
mcuio bitbang i2c: make it possible to override regular udelay()
arch-atmega: avoid udelay for i2c (no reliable udelay found for such short times)