Add importer for CDSS.

[qwandor]

Fixes #192.

[codecov]

Codecov Report

Attention: 121 lines in your changes are missing coverage. Please review.

Comparison is base (46960b7) 29.31% compared to head (dfc3c01) 28.29%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #274      +/-   ##
==========================================
- Coverage   29.31%   28.29%   -1.03%     
==========================================
  Files          25       27       +2     
  Lines        2906     3008     +102     
==========================================
- Hits          852      851       -1     
- Misses       2054     2157     +103     

Files	Coverage Δ
src/importers/balfolknl/mod.rs	19.33% <ø> (-9.02%)	⬇️
src/main.rs	6.58% <0.00%> (-0.25%)	⬇️
src/importers/icalendar_utils.rs	60.97% <60.97%> (ø)
src/importers/cdss/mod.rs	0.00% <0.00%> (ø)

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