Add a 'version' option, so that a version can be specified to 'finddeps'

The ability to specify a version is useful since some software relies on specific versions of cpan modules. If the cpan module is not present for the specified version, an error is thrown as normal; but if it does exist on CPAN, that particular version is pulled instead of the latest to ensure compatibility with the software.
This section is the doco for the returned objects. Doco for the arguments to finddeps lives in shared/parameters and gets inserted into the module by Evil Magic when I 'make dist' in preparation for uploading it to the CPAN