'-k' is short flag for milliseconds.
Cummulitive duration should be possible based on multiple arguments.
Partially confirms to specification. Many thanks to 'optimist' module.

- Milliseconds, seconds, minutes, hours values are taken as input.
- As per convention, long as well as short flags are allowed. e.g -s or --seconds
- Cummulative values for total duration possible. '-k500 -s2' will yield
  2500 milliseconds as total duration.
- '--help' is supported. See comments in code for more.
- Many TODOs added as well. See comments in code for more.
- Updated package.json