Added short multi option to docstring
Number of parallel processes now limited based on processor count
Can now specify number of processors to use with '-m' option.

When using the '-m' option, must specify the number of processors
to use (like '-m 4'). This limits the number of processors used at
a time by CanSen. Alternatively, if '--multi' is specified, CanSen
uses the available number of processors by default.
Fixed minor bugs in last commit