Try to make description clearer

I have always been a bit confused by the construction of the first sentence. It emphasizes things in a way that is hard for me to understand.

I took the description from the D3 site and tried to describe the benefits of elm-d3 in a simpler way.

I also got rid of the word pure because I don't want to use that in Elm branding. For people outside of Haskell, the term "pure" has come to point to something cultish, bringing to mind things like chastity belts and a holier-than-thou attitude. And when you look it up without knowing anything about Haskell, the first question is "how can a pure language do anything?!" which I think points to a problem with the term in the first place. I'd like to reframe this stuff as "managed effects" or "computations" or whatever. Something that does not have mixed brand association and that gives a clearer view of why it's an important property. In any case, I deemphasized this whole thing.