add coveragerc
fix dir for html report
don't test whether the orbit integration library fails to load
add html dir to gitignore
don't test normalize keyword (bc. normalize is tested differently; instantiate some special cases of potentials to make sure they're covered
don't test normalize keyword (bc. normalize is tested differently
don't cover AttributeErrors for Potentials
test vcirc in normalize
add tests of dvcircdR, omegac, epifreq, and rl
start on plotting tests for Potential