Adding keys fn to get all the log entry keys

[athos]

It's sometimes useful to be able to get all the log entry keys stored in a session without completing the log entries, especially for programmatically managing log entries.

(require '[postmortem.core :as pm])

(defn f [x]
  (pm/dump :args)
  (pm/spy>> :ret (inc x)))

(pm/keys) ;=> #{}

(f 42)
;; pm/keys never triggers completion of log entries
(pm/keys) ;=> #{:args :ret}
(pm/completed? :args) ;=> false
(pm/completed? :ret) ;=> false

;; while pm/logs does
(pm/logs) ;=> {:args [{:x 42}], :ret [43]}
(pm/completed? :args) ;=> true
(pm/completed? :ret) ;=> true

This feature adds a new method to ILogStorage, which comes with a minor breaking change only a few users (if any) may be affected.

[codecov]

Codecov Report

Merging #4 into master will decrease coverage by 0.12%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master       #4      +/-   ##
==========================================
- Coverage   91.79%   91.66%   -0.13%     
==========================================
  Files           7        7              
  Lines         329      336       +7     
  Branches       16       17       +1     
==========================================
+ Hits          302      308       +6     
  Misses         11       11              
- Partials       16       17       +1

Impacted Files	Coverage Δ
src/postmortem/protocols.cljc	100% <ø> (ø)	⬆️
src/postmortem/session.cljc	93.97% <100%> (+0.22%)	⬆️
src/postmortem/core.cljc	85.22% <75%> (-0.49%)	⬇️

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