Remove deprecated features and FutureWarnings

[Jakob-Unfried]

Removing support for deprecated features, FutureWarnings, etc.

I am heavily using rebase and force push on this branch, to get a clean commit history.
If you want to base anything on the commits in this branch, let me know, so i can be considerate of your history...

Wait with merging!

Should wait for all other features of release 1.0, then release a version 0.99 which includes all those features but still hast the FutureWarnings and backwards compatibilities.
Then we merge this PR on top of 0.99 to release 1.0.

Plan

• Go through the explicit checklist in FutureWarnings to be removed #47
• Search for FutureWarning
• Search for .. deprecated ::
• Search for uses of Config.deprecated_alias
• changelog
  • Have a WIP version that lists all current changes.
  • Nice rst formatting
  • todos in the v1.0.0.rst file

TODO list / single issues:

• test_mps generates warnings?
  • It also does on the current main branch, so i did not introduce this here, see Test coverage #240 .
• Is FutureWarning filtering in the tests, e.g. in test_np_conserved.py via warnings.simplefilter("ignore", FutureWarning) still intended? (also in test_hdf5 and test_pickle)
• fix doctests
• CouplingModel.add_coupling arguments

[Jakob-Unfried]

@jhauschild
There is one open questions from my side, see below.
Otherwise the PR looks done to me, except for the changelog, which we will touch up anyway, when we are ready to release.
Could you review anytime before v1.0.0?

There is a deprecation notice in the docstring of models.CouplingModel.add_coupling:

tenpy/tenpy/models/model.py

Lines 1008 to 1009 in 8c8e8db

	.. deprecated:: 0.4.0
	The arguments `str_on_first` and `raise_op2_left` will be removed in version 1.0.0.

I am not sure why those arguments should be removed?
Also, we have not issued warnings so far, so just removing the args would be quite harsh.