Add tests for LOC record String() generation and fix small problems

Added tests for the cmToM function to make sure that it's output is
correct. Modified the way the Altitude is written to a string. Previously,
if the altitude was an exact number of meters it would always be reported
with two decimal places. This is not needed. Conversely if it was not
an exact number of meters the cm were removed.
Merge pull request #158 from FiloSottile/loc_fixes

Add tests for LOC record String() generation and fix small problems