Revert "started on STDIN functionality, removed support for multiple files (csvkit will do handle this)"

This reverts commit c4d24feca24f978aa9032dce8dd45482c1c6e3c4.
Revert "Revert "started on STDIN functionality, removed support for multiple files (csvkit will do handle this)""

This reverts commit 422d2907ae651c1564addee819a5e0453d47f14e.
Merge branch 'stdin_funcs' of github.com:datamade/dedupe-csv into stdin_funcs