components : change IO pins of pid to IN

it was not possible to connect an IO pin to another writing pin
for example "net signal mux2.0.out pid.0.bias"

changed were:
Pgain
Igain
Dgain
FF0
FF2
deadband
maxerror
maxerrori
maxerrorD
maxcmdD
maxcmdDD
bias
maxoutput
docs : update manpage pid.9 for use of IN pins
Merge pull request #226 from luminize/input-pins-for-pid

components : change IO pins of pid to IN