Moving test files around, adding externs for underscore 1.4.4
Bugfix for 1.4.3 externs: typo in `properties` param for _.where
Bugfixes for underscore 1.4.3 externs: adding `Arguments` params.
A bunch of functions that operate on arrays can also operate on
Arguments objects.
Updating README to note availability of 1.4.4 externs.