PySDM v3.0.0-pre.1

What's Changed

• docs: add a note on units to the PySDM docs landing page by @slayoo in #1671
• add checks for broken links in markdown files, docstrings, notebooks, etc by @AgnieszkaZaba in #1672
• docs: add acknowledgement for M3ODEL funding by @slayoo in #1675
• add "threshold" homogeneous freezing & refactor immersion/homogenesous freezing setting flags + new thaw logic + GPU support for homogeneous freezing + removal of paper .md files in anticipation of 3.0-preX releasing scheme + update in copula examples to match changes in pyvinecopulib API by @tluettm in #1665

note: since in #1665, we've introduced API-breaking changes (naming of parameters in Freezing dynamic constructor), we are introducing v3.0.0-pre.N version numbering. Please expect a dozen of -pre.N releases overt the next months, before we roll out PySDM v3.

Full Changelog: v2.131...v3.0.0-pre.1