Batch generation --all-documents

[sandorfr]

Have a --all-documents switch to actually output all swagger documents or make it the default behavior when no document is specified instead of using the default v1 value. This would allow users to output all their swagger api documents at once.

By the way --swagger-api-version might not be the right name and may be benefit from being renamed to --swagger-document as some people might split their API accross different files, for instance some API might be targeted at different audience and one might want to generated clients/documents scoped on a specific API area.