Dclab

- feat: allow to register external look-up tables for Young's
modulus computation (88)
- ref: restructure look-up table file handling
- ref: deprecated [calculation]: "emodulus model" metadata key in favor
of the more descriptive "emodulus lut" key.
- ref: the "method" argument in the context of isoelasticity lines
is deprecated in favor of the "lut_identifier" argument

- fix: writing "filtering" and "calculation" metadata sections
to .rtdc files should not be allowed

- ci: fix rtd builds
- ci: fix PyPI releases

- ci: migrate to GitHub Actions

- enh: add soft type check (assertion) for "emodulus medium"
key in ancillary features (86)
- fix: make sure that strings are not written as bytes in
hdf5 files

- enh: add boolean "model converged" key to return dictionary of
`Rlme4.fit` (85)