Adds yesod-simple-rio template

[cdornan]

CF: yesodweb/yesod#1602
CC: @snoyberg

This template takes yesod-simple and replaces classy-prelude-*
with rio. I have checked that everything builds and runs out of the
box, and that the tests are green.

I have not (yet) used it in anger to develop an app, and I am but a
Yesod and RIO neophyte, so it needs careful reviewing.

Some points:

• bounds on aeson and yaml were relaxed to allow those in the
  latest lts release (13.25);
• http-types, yesod-newsfeed and persistent was added with
  no bounds restrictions — what restrictions should we use
  on these packages?
• rio >= 0.1.8.0 : is my starting point — can we relax the
  upper bound? What upper bound should we use?
• To get rio to work with the current stack I am hiding parts of the
  rio logging system (I guess these will be addressed by
  this work).

[snoyberg]

Sorry, I should have pointed out earlier: it would be best to have a PR against https://github.com/yesodweb/yesod-scaffold/ instead. I'll ultimately be removing the Yesod templates from this repo.

[cdornan]

@snoyberg should the template file to go in the root folder? (Stack would like that I guess.)

[snoyberg]

I generate the template files from that repo. Check out the simple branch, for example:

https://github.com/yesodweb/yesod-scaffold/tree/simple

[cdornan]

@snoyberg Ahh I see now — sorry for being a bit dopy — I have converted this into a PR on yesod-scaffold: yesodweb/yesod-scaffold#194