Add severity as sentry_logger's breadcrumb hint

[st0012]

This will allow users to filter sentry_logger's breadcrumbs with log level like:

config.before_breadcrumb = lambda do |breadcrumb, hint|
  if severity = hint[:severity] && severity <= 1 # debug & info
    nil
  else
    breadcrumb
  end    
end

[codecov-commenter]

Codecov Report

Merging #1527 (ca0cc59) into master (1a47151) will increase coverage by 0.55%.
The diff coverage is 100.00%.

❗ Current head ca0cc59 differs from pull request most recent head f3794a8. Consider uploading reports for the commit f3794a8 to get more accurate results

@@            Coverage Diff             @@
##           master    #1527      +/-   ##
==========================================
+ Coverage   98.20%   98.76%   +0.55%     
==========================================
  Files         218      123      -95     
  Lines       10608     6779    -3829     
==========================================
- Hits        10418     6695    -3723     
+ Misses        190       84     -106     

Impacted Files	Coverage Δ
sentry-ruby/lib/sentry-ruby.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/breadcrumb/sentry_logger.rb	100.00% <100.00%> (ø)
...-ruby/spec/sentry/breadcrumb/sentry_logger_spec.rb	100.00% <100.00%> (ø)
...ntry-raven/lib/raven/helpers/deprecation_helper.rb
sentry-raven/lib/raven/instance.rb
...en/spec/raven/integrations/rails/activejob_spec.rb
sentry-raven/spec/raven/integration_spec.rb
sentry-raven/lib/raven/linecache.rb
...c/raven/processors/removecirculareferences_spec.rb
sentry-raven/spec/raven/instance_spec.rb
... and 88 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1a47151...f3794a8. Read the comment docs.