rework and vastly expand the MIR section#67

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mark-i-m merged 4 commits intorust-lang:masterfrom

nikomatsakis:mir-nll

Feb 28, 2018

Commits on Feb 26, 2018

Commits on Feb 27, 2018

fix typo
nikomatsakis
committed

Commits on Feb 28, 2018

address nits
nikomatsakis
committed