Fixed spelling, fixed formatting of an error message.

Hello!  I fixed some little things in the ferret gem.  Please consider merging this into the next version.  The two commit messages I wrote should explain it pretty well, but let me know if you would like more explanation.

Also, is Dave Balmain really the author anymore?  It seems like a lot of things on the front page of https://github.com/jkraemer/ferret could be updated.

--David