Fix Cat.sleep()

[kurtlindberg]

Additional patches to Issue #10

pyCatSim/pyCatSim/api/cat.py

• 'duration' argument in Cat.sleep() changed from an optional argument (default=0) to a required argument

pyCatSim/pyCatSim/tests/test_api_Cat.py

• added assertion for test parameter where increase in cat.energy is greater than 0 in TestcatCatSleep.test_sleep_t0()

[khider]

test not passing

[kurtlindberg]

Will resubmit PR later through an updated fork of pyCatSim