Impedance

Fixes a bug in the Randles circuit class circuit definition 🐞

Big thanks to lucasfdvx for the bug report ⚡ and BGerwe for the fix 🛠️

- adds the `weight_by_modulus` option for makinig fitting spectra easier 🏋️ stephendkang
- improves the documentation and uses the new GitHub citation feature 🐧 petermattia hkennyv
- transitions CI to use GitHub Actions instead of TravisCI 📦 ml-evs

As always, you can update via `pip install --upgrade impedance` ⛲

Big thanks to petermattia for contributing to this update!

- Adds convenient method for saving (and reading) impedance data to .csv files 🖨️
- Improves the basinhopping global optimization functionaliity 🪂
- Standardizes the circuit element code format ☕

As always, you can update via `pip install --upgrade impedance` ❇️

Adds bounds to the global optimization fitting functions 🏖️

Patches a bug with passing kwargs from circuit.fit to the new global optimization function 🐞 🐞

Adds a global optimization option (via scipy.optimize.basinhopping) for fitting equivalent circuits 🌍 thanks petermattia

As always, you can update via `pip install --upgrade impedance`! 🔋