Revision history for RPi-HCSR04

2.3603  2017-08-04
        - modified tests with env var RPI_HCSR04, so that we don't test when it
          isn't feasible

2.3602  2017-07-07
        - revert out the loop in XS. Forgot about the warning
        - modified XS so that _cm() and _inch() each do their own business;
          _cm() doesn't call _inch() anymore

2.3601  2017-07-07
        - added github info to Makefile.PL (closes #3)
        - corrected pin numbers in voltage divider section in POD (closes #4)
        - removed 'sudo' requirement from POD (closes #6)
        - renamed all C functions to private, and removed POD that outlined them
        - added '-lrt' to Makefile.PL LIBS to avoid undefined 'shm_open' symbol
        - changed version numbering scheme to be in line with what other of the
          RPi dists use that require the wiringPi library (closes #7)
        - put warning in place that the end-user needs to do timing in loops
        - loop in C until we get a value that is within range (0cm-400cm)
          (closes #1)

0.02    2017-01-13
        - POD updates

0.01    2017-01-13
        First version, released on an unsuspecting world.

