Add reference implementation of a BMP085 driver

Some notes:
* I did a straight conversion from the Bosch C implementation to C++ for use
  with Arduino.  NB: I did _not_ refactor the implemntation to make it more
  object-oriented, and there are aspects regarding that that could use some
  attention.  I just wanted a reference implementation from Bosch.
* Cleaned up the code a bit.  Again note that I didn't try to eliminate
  magic numbers or unmeaningful variable names -- I just try to reformat
  it to make it a bit more readable.
* I made no changes to the original implementation to try to optimize
  for size.
* Original implementation taken from revision 1691:
  http://svn.code.sf.net/p/bosch-ros-pkg/code/trunk/stacks/bosch_drivers/bmp085/