formula for platypus cli

New formula for Platypus:
http://sveinbjorn.org/platypus

Note that this is for the cli only, which installs as 'platypus'.
Update Platypus formula.
Add caveats.
Remove redundant version number.
Install a couple more essential components.
Minor cleanup.
Use cd command.
Build within buildpath.
Remove redundant cd.
Merge branch 'platypus' into frescobaldi-platypus
Create launcher.
Make launcher .app optional.
Remove redundant dependencies.