Document Client and Scope classes.

[st0012]

This is part of #1636

[codecov-commenter]

Codecov Report

Merging #1659 (3f75736) into master (ad4828f) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1659      +/-   ##
==========================================
- Coverage   98.51%   98.48%   -0.03%     
==========================================
  Files         136      136              
  Lines        7671     7672       +1     
==========================================
- Hits         7557     7556       -1     
- Misses        114      116       +2     

Impacted Files	Coverage Δ
sentry-ruby/lib/sentry-ruby.rb	94.28% <ø> (ø)
sentry-ruby/lib/sentry/scope.rb	100.00% <ø> (ø)
sentry-ruby/lib/sentry/client.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/background_worker.rb	94.59% <0.00%> (-5.41%)	⬇️

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