Version 1.3

Merge pull request phoenixframework#501 from phoenixframework/readme_…

…revisions

Several Readme.io suggested edits

Update acrhive url

Merge branch 'master' of github.com:lancehalvorsen/phoenix-guides

suggestions from the site

Merge pull request phoenixframework#141 from lancehalvorsen/refurb-ch…

…annel-guide-090

Refurbish Channel Guide for Phoenix 0.9.0

suggested fix from phoenixframework.org

first pass at a real mix tasks guide