Add MultipleTsvFiles input source.

Allows you to specify an array of file paths that have the
correct Tsv schema. Includes a new test case for this source.
Don't use multiple parameter declarations

Pass in a Sequence of paths instead of varargs so that we can have
a single parameter list
Merge pull request #460 from rweald/add_multiple_tsv_input_path_source

Add MultipleTsvFiles input source.