Initial pass to porting to /bin/sh

Switches shebang to /bin/sh, substitutes double-bracketed conditional
checks for single-brackets ones, and replaces brace expansions with just
a regular wildcard character.
Target leading slash checks

Replaces this with a case statement rather than a regular bracketed if
check, with the former being portable and the latter not.
Target 'addons' substring check

Also replaces this with a case block to be interpreted correctly on
regular /bin/sh.
Missing MP3 file during installation/packaging

Both the install and package script should include the MP3 file from the
source directory.

This fix must be backported via a cherry-pick to the pre/v1.0.0 branch.
Switch packager to check for zip extension later

This brings this script in-line with the others in that it will now
check for the zip extension only after the existence of the parameter
has been checked.
Use single quotes consistently

These should be used whenever variable interpolation is not needed.
Fix for packaging MP3s

We only want the MP3 from the top-level awesometts package -- do not
include anything from the cache directory.
Merge branch 'chg/sh-scripts-42' into develop

Closes #42.

Conflicts:
	addon/tools/package.sh  (mp3 change, took branch version)