RF: Promote internal status() helper with docs, and breadth-first reporting

[mih]

Matching the diff_dataset() helper.

I had this change lying around locally. it makes using status-functionality internally more convenient.

[mih]

I tried to convince the one mac runner on appveyor to actually do something but failed 5 times. The nature of the change makes it highly unlikely to fail only in this one particular run. Hence I'll ignore it.

[codecov]

Codecov Report

Merging #6006 (a43d41a) into master (a50434e) will decrease coverage by 0.00%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #6006      +/-   ##
==========================================
- Coverage   90.16%   90.16%   -0.01%     
==========================================
  Files         315      315              
  Lines       42188    42196       +8     
==========================================
+ Hits        38040    38047       +7     
- Misses       4148     4149       +1     

Impacted Files	Coverage Δ
datalad/core/local/status.py	94.16% <75.00%> (-2.27%)	⬇️
datalad/support/tests/test_annexrepo.py	97.61% <0.00%> (+0.14%)	⬆️

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[mih]

OK, more docs should be more good