support stdin parsing

[minhtrancccp]

currently, play requires to have the input data saved in a file before reading it with a tool. as far as i know, most (if not all) of the supported tools by play provides parsing from stdin, which lets user pipe data to such tools. it would be great if play also support parsing data that way, e.g. by letting user invoke the tool with play [tool] - (i.e. specifying a dash to read from stdin).

[paololazzari]

This has been on my to-do list for a while, will work on it soon