Further clarify/simplify event/interrupt map usage.

This furthers the changes started in fbb1fb0027b827ecbbb34dca18270b7cac8fcbb1.
prussdrv_pru_clear_event and prussdrv_pru_reset_interrupt now explicitly only
clear the event and reset the host interrupt line.  As indicated in
8bfab8826e7800721cf7f6aecdb779a47a17ded2, the order of these operations is
critical so-as not to falsely re-trigger the host interrupt (see See Section
6.4.9 of Reference manual).

This change also adds a function **prussdrv_pru_reset_event**.  This function
first clears the event specified by the user and then resets the host interrupt
line to which the specified event is tied (no need for the user to also specify
the host interrupt line).
bring HMR register names in line with datasheet
Finish clarify/simplify event/interrupt map usage.

This is an aggressive attempt to bring the software both in-sync with the
datasheet as well as clarifying and simplifying the event/channel/interrupt map.
This finishes(hopefully?) the changes continued in
910111e4a334c53be8e2f8e812d8988423af98cc.
add library of very basic useful macro defs for pasm code
Update examples to use pasm -Idir and clarified events/interrupts