Added option for substring-language-evaluation (read desc.)

I liked this tweak the instant I saw it so much I had to get out of bed to add some much needed functionality. 

It currently evaluates the whole textarea which makes it less useful for me - who sometimes writes a paragraph in english and then something in swedish. So this pull request adds an option for just that. With the option set to ON it will only read the last 15 characters on the textarea meaning that if you write 1000 words in english it will still change to swedish after only a little while because it only sees the swedish words in the substring.

This have got some bugs though so I'd recommend you to just look over it and see if it is something you'd like incorporated.

Some notes:

1. For some reason - the "loadPrefs" method is called many times when I change an option. I think this has to do with the fact that the bundle is "com.apple.UIKit" (I am not sure though). This is not very important though as users does not change settings very often.

2. It only looks at the absolute last part. Meaning that if the user writes in one language at the bottom and then goes back to the top to write another - it will not change. Can I get the caret position somehow? 

3. The icon is fugly (for the settings-entry).

4. I had to remove some things in the makefile (arm-things) to get it to compile in my env.

Feel free to read through everything and give me some feedback on this.