* Rename `reflectance` to `dimensionless_albedo`
* Use disk-integrated albedo (product of geometric albedo and disk-integrated phase function) rather than disk-average bidirectional reflectance
* Add conversion between albedo and cross-section with a given total flux/magnitude
* Updated docstrings and doctests
* Add optional parameters `rh` and `delta` for future implementation.

* Update test data with the new albedo definition (albedo = reflectance * pi)
* Add tests for `albedo_unit`
* Add tests for convertion between albedo and size
* Expand tests to cover the conversion in both directions for all cases
* Replace np.isclose and np.allclose by u.isclose or u.allclose

Including all tests and remote tests.