add multiple report format output at once

[jcarnu]

-this is the text from #1826 -

Hello,

ora2pg generates reports in multiple formats with -t SHOW_REPORT . Those formats are mutual exclusives at run time and there's no other way to generate multiple formats outputs at once.

Proposition:

The project is not to modify ora2pg behaviour but having a "file-prefix" switch allowing multiple output files target : --dump_as_file_prefix=db-report used in conjunction with --dump_as_html and --dump_as_json should generate db-report.html and db-report.json files with the corresponding format.

I'll provide a patch just after submitting this improvement.