Better Error Handling in CSV

[jberger]

Currently the errors emit with location/line numbers from within the plugin. It would be better if that could come from caller's stack if possible, though Text::CSV doesn't use Carp so that isn't easy. Failing that it should probably strip the line numbers. It also would be nice if it could be in either a more raw textual format, getting an HTML error when requesting CSV isn't totally pretty.

These issues were apparent when working on #7