Arc-alkali-rydberg-calculator

Checking new CI pipeline

Minor release:
- fixes (64 61)
- provides selection of units for plots (65, contribution by Peter Mao)

Minor update:

- Added low-lying data for Ca and Yb from NIST database (7a5468844a80a5a6b96ee6842611e4ff31231d34, eb9a185922b4e9ebc25f8b9780db633519e5e8d7)
- Updated Rb-85 quantum defects for g states (more precise experimental values are now available) (c3ae0eb0b8479bdfc6b027b0c1a93c75ed637173)
- Fixed picker issue under new matplotlib version for interactive plots (4dbdaf107ef1d3990557a073f305e4a23518aa6a)

Minor bug fixes:
- when calculating `StarkMap` for very low lying states, it is possible now to include `nMin` below ground state, and ARC will add then to the basis states whose principal quantum number is below the ground state p.q.n, but whose energies are above the ground state energy (b42c72bceacfd93d7c13e77f1ae62a38cb4532e6).
- fixed `DynamicPolarizabilty` for J=0 states: before in calculation tensor polarisability ValueError would be emitted, but now it just correctly returns 0 for tensor polarisability (421bf8cb6a4668fc72c6727d3197cb0a423d8e9e).

Major release.

Adds support for **divalent atoms** and new methods for working with atom-surface interactions, for modelling ultracold atoms in optical lattices and for calculating valence electron wave functions and dynamic polarisabilities. [Check preprint arxiv:2007.12016 for more details](https://arxiv.org/abs/2007.12016). New [example notebook](https://arc-alkali-rydberg-calculator.readthedocs.io/en/latest/getting_started.html#ipython-notebook-with-examples) is also available.

Fixes installation issue of 2.2.0 (missing refractive_index_data folder 36 ).