ENH: add DataFrame anonymizer
Often on SO people looking for help say they can't put their DataFrame somewhere for others to look at because the data's private.  In most cases, the data itself isn't relevant to answering the question, and only the structure matters.

It would be straightforward to add a method which replaces string data and index/column names by A,B,C, randomizes numbers and times (with or without preserving the overall ordering), etc.  There's a reasonably popular [R question](http://stackoverflow.com/questions/10454973/how-to-create-example-data-set-from-private-data-replacing-variable-names-and-l) asking about the same.
