Make sending and logging safer

[marcomorain]

• Inject a send-fn that is used to send items, rather than changing behaviour based on the presence or absense of a token.
• Enclose more of the sending process in a try/catch.
• Move logging deeper into the callstack.

[codecov[bot]]

Codecov Report

Merging #20 into master will increase coverage by 2.17%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   95.07%   97.24%   +2.17%     
==========================================
  Files           2        2              
  Lines         142      145       +3     
  Branches        5        3       -2     
==========================================
+ Hits          135      141       +6     
+ Misses          2        1       -1     
+ Partials        5        3       -2

Impacted Files	Coverage Δ
src/circleci/rollcage/core.clj	97.05% <100%> (+2.32%)	:arrow_up:

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