Change IN_BREAK variable logic.
Allow variable defaults to be overridden.
Exit INT and TERM signals cleanly.
Move trap outside of while loop.
Report totals at each period change.
Use the appropriate convention for bash booleans.

This is a proper fix for issue #2. The double bracket convention does
not work when using true and false for bash booleans.
Revert to previous flag toggle method.
Updated README to reflect new features.
Commentation and cleanup.
printf time left message to terminal tab