Documentation edits

Edit the documentation for minor grammar, idiomatic usage, and sentence construction issues.  Overall the documentation is great;  this is just cleaning up some places that sound a little odd.

There are some notes left in the documentation delimited by [bwb: ...] where I made a larger-than-usual change or I thought needed attention from someone more familiar with the codebase than I am.


I was taught to use two spaces in my typing class a  Long time ago. Two spaces is no longer the current fashion, and I've found it to be a tough habit to change. 

> On Nov 4, 2014, at 2:30 AM, Christian Kaps <notifications@github.com> wrote:
> 
> In docs/how-it-works/actions.rst:
> 
> > @@ -234,11 +234,10 @@ precedence over the global fallback.
> >  Handle Ajax requests
> >  --------------------
> >  
> > -If you send Ajax and normal requests to your Play app, then you should
> > -tell your app that it should handle Ajax requests differently, so that
> > -it can respond with a JSON result, for example. There are two different
> > -methods to achieve this. The first method uses a non-standard HTTP
> > -request header. Then on the Play side you can check for this header and
> > +Applications that accept both Ajax and normal requests should likely provide
> > +a JSON result to the first and a different result to others.  There are two different
> Between "others." and "There" are two spaces.
> 
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