Worked example of OAuth + shiny

[hadley]

• Start from https://gist.github.com/jcheng5/44bd750764713b5a1df7d9daf5538aea
• Refactor httr as needed to avoid duplicating existing OAuth code.
• Final product will be sample app passed on to shiny team

[hadley]

Gist at https://gist.github.com/hadley/144c406871768d0cbe66b0b810160528