Improve version detection & change DSN

[tlambert03]

This changes the SENTRY_DSN to use the new napari organization I set up.

It also detects whether napari is installed in editable mode, and tries to use the git sha.

also adds more docstrings in general

[codecov]

Codecov Report

Merging #4 (bc1c844) into main (50a48ef) will decrease coverage by 4.88%.
The diff coverage is 70.73%.

@@            Coverage Diff             @@
##             main       #4      +/-   ##
==========================================
- Coverage   99.53%   94.65%   -4.89%     
==========================================
  Files           3        3              
  Lines         215      243      +28     
==========================================
+ Hits          214      230      +16     
- Misses          1       13      +12     

Impacted Files	Coverage Δ
napari_error_reporter/_util.py	87.87% <66.66%> (-12.13%)	⬇️
napari_error_reporter/__init__.py	100.00% <100.00%> (ø)

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