Make our Rack pipeline a simple class abstracted from the App.
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Reload MM on environment and helpers_dir changes. Closes #1274. Closes #1105
Merge pull request #1315 from Arcovion/v3-stable

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Update README.md
bump aruba dep
Merge branch 'v3-stable' of github.com:middleman/middleman into v3-stable
merge
refer to v4 in readme
Merge pull request #1314 from middleman/rack-out

Untangle Rack from Application
Experiment with Contracts