Updating collision_rate_electron_ion in terms of collision_frequency. Currently the test for passing a custom velocity fails. Also if 'e-' is passed instead of 'e' that fails because collision_frequency is not robust and incorrectly chooses the ion-ion case instead of electron-ion case.
Updating collision_rate_electron_ion in terms of collision_frequency. Currently the test for passing a custom velocity fails. Also if 'e-' is passed instead of 'e' that fails because collision_frequency is not robust and incorrectly chooses the ion-ion case instead of electron-ion case.

StanczakDominik/PlasmaPy