Created a README and have the homepage point to that.

Dear maintainer of Parsec.

Since Daan's homepage for Parsec is both quite outdated and removed, I thought it was time to create a new "home" for Parsec. And the new thing is doing so by a REAMDE.md on Github. The target audience is people who are not fluent with Parsec yet, so I tried to include some beginners resources.

In addition to adding the README (and removing the prologue.txt) I also had the cabal homepage property point to the new "Github home".

I think Parsec is an amazing library and I hope that this way it can become a little less mysterious to new comers. To this extend I have some more "changes" in mind (like using less academic/technical terms to describe Parsec in the README and haddock -- if you are interested in this we can discuss it and/or I can make another pull-request with the suggested changes.

Have a nice day!