Cannot parse some unit strings from `scipy.constants` about units

[SimonHeybrock]

Here is a full list of the constants defined in scipy.constants (same as https://physics.nist.gov/cuu/Constants/Table/allascii.txt) that cannot be parsed (I give the unit in square brackets):

atomic mass unit-hartree relationship [E_h]
electron volt-hartree relationship [E_h]
Faraday constant for conventional electric current [C_90 mol^-1]
hertz-hartree relationship [E_h]
inverse meter-hartree relationship [E_h]
joule-hartree relationship [E_h]
kelvin-hartree relationship [E_h]
kilogram-hartree relationship [E_h]
natural unit of momentum in MeV/c [MeV/c]
Newtonian constant of gravitation over h-bar c [(GeV/c^2)^-2]
natural unit of mom.um in MeV/c [MeV/c]

[phlptp]

I will work on adding support for those

[phlptp]

Added E_h and support for conventional electrical units. The units with 'c' in them I am still debating what to do.

also fixed J mol^-1 K^-1

[phlptp]

ok, I am going to add a UNIT_USE_COOKING_UNITS flag which would shift some units to the cooking abbreviations but default to the science units. This enables the use of 'c' as the speed of light, which I think should fix your issues. Need to do a bit more testing and add the docs but I should have a PR by Monday