Prep 0.7.7

[ivirshup]

Prepping 0.7.7 bug fix release

Urgent because new scipy breaks SparseDataset indexing

• Re-organize docs to be like scanpy
• Update build
• Update release notes to be more like scanpy wait for town crier?
• Finalise release notes
• Decide whether we are hiding experimental for the release (yes)

[codecov]

Codecov Report

Merging #639 (1b5ef78) into master (63d40ff) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #639      +/-   ##
==========================================
+ Coverage   83.36%   83.38%   +0.02%     
==========================================
  Files          30       30              
  Lines        4142     4135       -7     
==========================================
- Hits         3453     3448       -5     
+ Misses        689      687       -2     

Impacted Files	Coverage Δ
anndata/_core/merge.py	93.25% <ø> (ø)
anndata/_metadata.py	64.28% <ø> (-1.43%)	⬇️
anndata/__init__.py	100.00% <100.00%> (ø)