CCR code: Change to sample structure

1) All the variables in the sample structures are strongly typed
2) Two additional types were declared in units.h:
     o2pressure_t
     bearing_t
3) The following variables were added:
     diluentpressure
     o2setpoint
     o2sensor[3]
4) Changes to a number of files were made to chanf
     sample->po2 to sample->po2.mbar
     bearing to bearring.degrees

Signed-off-by: Willem Ferguson <willemferguson@zoology.up.ac.za>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
When calculating the maximum of unsigned values, use unsigned variable

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>