update README and add header file to package

	modified:   README.md
	modified:   yerba/__init__.py
add command line interface

The engine can now be monitored and managed using a command line
interface.

	modified:   bin/yerba
update submitted and completed times

Reset the jobs completed time and submitted time if the job is
restarted. When the job is cancelled set its completed time.

	modified:   yerba/db.py
	modified:   yerba/managers.py
remove verbose error checks from logging functions

	modified:   yerba/workflow.py