Solo-epd-loader

<!-- Release notes generated using configuration in .github/release.yml at v0.2.1 -->

What's Changed
Bugfixes 🛠
* Extend readme for STEP electron data (fix 21) by jgieseler in https://github.com/jgieseler/solo-epd-loader/pull/24


**Full Changelog**: https://github.com/jgieseler/solo-epd-loader/compare/v0.2.0...v0.2.1

What's Changed
Bugfixes 🛠
* Fix v1.24 deprecation of np.object
* Set loading level 2 data (`level='l2'`) as default (14)
* Obtain FILLVAL dynamically (7)
New Features 🎉
* Add support for new (since Oct 22, 2021) STEP data product (5)
* Columns in returned DataFrame have slightly different names compared to old data product
* Now electron data are automatically calculated and provided in returned DataFrame
* Data for all individual pixels are now provided in addition to the average over all
* New options for `epd_load()`:
* **only_averages**: bool, optional
If True, will for STEP only return the averaged fluxes, and not the data of each of the 15 Pixels. This will reduce the memory consumption. By default False.
* **contamination_threshold** : int or False, optional
If int, mask electron data that probably is contaminated (i.e., set it to nan) using an integer contamination threshold following the equation:
Integral_Flux - Magnet_Flux > contamination_threshold * Integral_Uncertainty
If False, don't alter the data at all. Only implemented for new STEP data (after Oct 2021) so far. By default 2.

**Full Changelog**: https://github.com/jgieseler/solo-epd-loader/compare/v0.1.11...v0.2.0

- Fixes 16: Replacing FILLVALUES not working with pandas 1.5.0

- Fixed a bug that occurred in Windows while loading STEP data, where `cdflib.cdfepoch.encode()` did not understand the type of the Pandas Dataframe index

- Fix some `cdflib` usage that could cause a bug when run in Windows

- Replace usage of `cdf2df()` from [HelioPy](https://github.com/heliopython/heliopy) with `read_cdf()` from [SunPy](https://github.com/sunpy/sunpy) for loading EPT and HET data files
- Obtain FILLVAL for STEP data dynamically (instead of hard-coded)
- More detailed description of caveats in the readme
- Bugfixes in example code in the readme