Adds TextSoap extension

Presumably also adds it to the site next time you build it, since I added the extension to the Index.plist, as well (note that I added this to the "text transformation" group, since that was the closest I could find to actually capture what the extension does). I couldn't find any information about how to sign the final .popclipextz package, so I left it a simple zip of the source.

Been using this extension for months, and haven't run into any trouble with it so far. Loving PopClip!

I also fixed several typos in the README that bugged me when referring to it. Spellcheck is a wonderful thing... ;-)