Added ability to reprex from an expression as an argument, closes #2. #6
Set up to work from a tempfile(), or to take an output filename as an argument, closes #4.
Added tests for clipboard read/write/copy and for a simple reprex example from the clipboard or from an expression.
This was, um, a lot of breaking changes. I probably should have started by adding the expression, then considering temporary and output files, but I found myself making both changes at once. We should definitely discuss issue #4 if you don't like the new approach, and I can extract it out from the other changes.
(Note that reprexing from an expression involved separating reprex into two functions, reprex and reprex_. This is loosely based on lazyeval's recommendations. The end user doesn't have to worry about reprex_ though).