Added SensorsPublisher node
Merge branch 'alecj' of github.com:alecjohanson/robot into alecj

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arduino, differential_drive, rosserial -> repo

These nodes have been moved from the DD2425_2013 folder to
our repository so we can edit them under version control.
Modified Arduino motor control

This is the first of some changes to the Arduino code
to allow better motor control and adjustment of the
controller parameters.
Made the arduino code much cooler

Changes:
The motor PI control is now done by a hardware timer ISR with exact
timings instead of whenever a ROS Speed message happens to arrive.
The raw encoder data is published whenever new values are read.
The quadrature decoder ISRs are now much faster, no more arduino library
overhead in there.
The arduino now accepts either Speed messages (switches it to PI control
mode) or PWM messages (switches to direct PWM mode). This may be useful
for testing, e.g. measuring the step response of the motors.

Caveats:
This code hasn't yet been tested. Signs may be wrong (encoder/motor
direction), the 50ms timer period may be suboptimal, something might not
work at all.
Arduino: Changed the ADC to interrupt-based
Modified Arduino: Motor control works (mostly)

Some more playing with the control parameters may be necessary.
Fixed some conflicts