Inconsistent timing of on_read/write() and on_input/output()

[kosarev]

We call on_read() and on_write() in the beginning of the cycle but seem to aim to call on_input() and on_output() at where they actually should happen within the cycle. Now that we are about to introduce something like on_wait() (see #10), which doesn't make much sense if is not being called at right cycle's tick, maybe we should fix the timing of on_read() and on_write() calls as well.