Major bug fix for getUsage()

Fixed: getUsage not return limit

- Implemented `getUsage` method
- Added additional parameter to include limit

Initial Release

This release contains the main features of Schedule Limiter such as;

1. constructor]
2. setLimit(id, limit)
3. getLimit(id)
4. setLimits(limits)
5. createSchedule(id, tokens [,force])
6. cancelSchedule(id, tokens [,force])
7. getUsage(id, months)

Also it's currently using Redis as database.