Upgrade launcher

[randomnetcat]

• Avoids shelling out for file manipulation.
• Adds parameter to set path to 7z executable, rather than always using the one in PATH.
• Adds parameters to allow passing through arguments to dumpgenerator.

[elsiehupp]

Hi Jason!

I do not have a good sense of what exactly these changes do, but I do welcome contributions like this! (I just sent you an invite to be a collaborator on this repository.)

Something that I think could help would be if you were to add a small section to the "Using dumpgenerator" section of the README to explain the added functionality and provide a sample command line string for using it (and also for reviewers here to test that it works).

Also please do add your name to the "WikiTeam Team" section of the README (which I should also rename because we're not officially affiliated with the WikiTeam organization at this point). (Honestly I should revisit the README more generally, but that's another issue...)

Thanks!

[randomnetcat]

Both done (and thank you for reminding me that I need to update my name here :P).