Refactor extract function 'install'
Define BUNDLED constant.
Define constants and install() only if BUNDLED.
Programatically determine path to installed DOSVOX.
Rephrase comments.
Refactor extract function run_launch_script()
Add missing return statement.
Refactor better comments and function names.
Rewrite run launch script branch logic.

Hopefully this is simpler and easier to reason about than before.
Exterminate arbitrary program return codes.
Run cheaper assertion first, fail ealier.
Refactor purify functions.
Verify that DOSVOX is installed.
Automatically add XMPPVOX to DOSVOX menu.

Closes #15.
Do not share 'args', not needed.
Handle KeyboardInterrupt in a broader scope
Generalize function to run ScriptVox scripts.

Rename launch script from "xmppvox.cmd" to "launch.cmd"
Change logic to assert we're running from within DOSVOX.
Add audible success/failure messages using ScriptVox.