Added filter options to timeEntriesByProject
Added filter options to timeEntriesByProject

I added the filter variable to the timeEntriesByProject.  It checks for the following in options parameters:
1. billable.
2. only_billed
3. only_unbilled
4. is_closed
5. updated_since
6. user_id

These are acceptable option parameters per the Harvest API documentation. http://help.getharvest.com/api/reports-api/reports/time-reports/

This was already done for timeEntriesByUser function below this one.
log0ymxm/node-harvest