Reimplement log/experimental_levels#470

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ChrisHines merged 8 commits intomasterfrom

Mar 3, 2017

Commits on Feb 21, 2017

log: More detailed benchmarks for experimental_level package.
ChrisHines
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Commits on Feb 23, 2017

log: Reimplement experimental_level package with a bit set.
ChrisHines
committed
Test that level values are correctly formatted in Logfmt and JSON.
ChrisHines
committed

Commits on Feb 24, 2017

Commits on Mar 1, 2017

log: Add level.NewInjector and export Key and [Level]Value functions.
ChrisHines
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Commits on Mar 2, 2017

log: Add docs for new types and functions.
ChrisHines
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Commits on Mar 3, 2017

Add clarifying sentence to NewInjector docs.
ChrisHines
committed