Fix the usage of scripts

[dachengx]

What is the problem / what does the code in this PR do

1. Move rechunker to strax/scripts/rechunker.py
2. Remove bin/ folder because it is incompatible with pyproject.toml
3. Add script of rechunker to pyproject.toml

Can you briefly describe how it works?

Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Please make sure that all automated tests have passed before asking for a review (you can save the PR as a draft otherwise).

[coveralls]

coverage: 90.228% (-0.6%) from 90.86%
when pulling d7fe6f1 on fix_script
into 66b66f4 on master.