Copy over progress code from shinyIncubator
Get session without needing to pass it in
Add Stack ref class
Put progress stack in session object
Simplify code
Improve handling of closed progress
Add missing 'var'
Use new message format for progress reporting
Unify binding and page-level progress interface
Simplify argument handling
Make progress bar show on top
Export Progress generator
Simplify R API for progress
Fade in bars
Update NAMESPACE
Make progressHandlers a simple object
Make progress position more customizable
Don't use multiline string in JS
Add container for all progress items
Fixes to file.path.ci

There were two bugs, which are fixed:
* It didn't find files starting with '.' because `all.files` defaults to FALSE.
* It was too loose with file matching - the `pattern` argument to list.files
  is a regexp, not string literal.