added z-index:-10 and settings multiWords: true

Hello polarblau,

I made two changes to jquery.suggest.js:

- I added z-index: -10 in the JS so that it works even if there is no CSS to set the z-index: +10 for the input. When I first used the plugin I thought it was broken because it did not work without the CSS.

- I added a new option multiWords which defaults to false (existing behavior) but when set to true allows autocompletion of the last word of the text. For example if I type "bla bla bla Py" it will autocomplete Py with Py[thon] and leave "bla bla" unchanged.