Prepare release v0.0.6.0

[andthum]

Prepare release v0.0.6.0

Type of change

• Change of core package.
• Change of scripts.

• Bug fix.
• New feature.
• Code refactoring.
• Dependency update.
• Documentation update.
• Maintenance.
• Other: Description.

• Non-breaking (backward-compatible) change.
• Breaking (non-backward-compatible) change.

Proposed changes

• Increase the version number of MDTools from 0.0.5.0 to 0.0.6.0.
• Update outdated links in the documentation.
• Correct the unit of the progress bar in the functions mdtools.dtrj.remain_prob and mdtools.dtrj.remain_prob_discrete.

PR checklist

• I followed the guidelines in the Developer's guide.
• [~] New/changed code is properly tested.
• [~] New/changed code is properly documented.
• The CI workflow is passing.

[andthum]

Test running MacOS-latest and Python 3.7 is failing due to an issue with the runner (see actions/setup-python#682).