Clean up the changelog for 0.2.0

[rcannood]

Describe your changes

Clean up the changelog before tagging v0.2.0:

• Fold the 0.1.1 section into 0.2.0, since 0.1.1 was never released.
• List the eight methods added since v0.1.0 under NEW FUNCTIONALITY, and fold the fixes made to them during the release candidates into their entry (with all PR numbers). BUG FIXES and MINOR CHANGES now only cover components that were in v0.1.0.
• Merge the two contradicting cellmapper_linear mask_var entries, and drop the ATAC peak sampling guard (Guard the ATAC peak subsample #35), which Select ATAC peaks by hvg_score and drop empty cells in process_dataset #78 superseded.
• Add the missing PR numbers (Add paramsets and include/exclude filters to run_benchmark #74, Select ATAC peaks by hvg_score and drop empty cells in process_dataset #78, Implement workaround for kernel ridge regression running out of memory #79, Restore the per-cell scale of senkin_tmp and ss_opm predictions #80, Fix/scbutterfly #81) and the missing entries for Updates to repository #15, Add denbi config and script #21 and Add authors Benjamin Frey and Vladimir Shitov #65.
• Move the --method_ids replacement to MAJOR CHANGES and the paramsets to NEW FUNCTIONALITY, and sort entries by component.

The v0.2.0 tag is on 4877c7fb in release/0.2.x, built before this PR, but the GitHub release notes use this text.

Checklist before requesting a review

• I have performed a self-review of my code

• Check the correct box. Does this PR contain:

  • Breaking changes
  • New functionality
  • Major changes
  • Minor changes
  • Bug fixes

• Proposed changes are described in the CHANGELOG.md

• CI Tests succeed and look good!