typos in Bradley-Terry model (https://github.com/stan-dev/example-models/blob/master/knitr/bradley-terry/bradley-terry.Rmd)

[nxskok]

Not indendently, but by using Markov chain Monte Carlo. - should read "independently". implicitly center the paremters around zero - should read "parameters".

[bob-carpenter]

It's super-easy to edit directly in the web interface and make a pull request. Want to give it a go, @nxskok?

I haven't finished that one yet, so there hasn't really been any proofreading.