doc: add topic - event loop, timers, `nextTick()`#4936

Merged

calvinmetcalf merged 19 commits intonodejs:masterfrom techjeffharris:doc-topic-event-loop-timers-nextTick

Apr 8, 2016

+467

Commits on Jan 28, 2016

doc: add topic - event loop, timers, nextTick()
techjeffharris
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Commits on Feb 17, 2016

update to address comments on PR
techjeffharris
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Commits on Feb 24, 2016

Commits on Feb 26, 2016

fixes suggested by @silverwind and @Fishrock123
techjeffharris
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Commits on Mar 25, 2016

Commits on Mar 29, 2016

update overview, phase detail headings, wrap at 72
techjeffharris
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Commits on Apr 7, 2016

Improve wording setTimeout() vs setImmediate()
techjeffharris
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