Add diagram of typeclass hierarchy

[rklaehn]

Not sure where the best place would be to put this. But I think it would be useful.

[codecov-io]

Current coverage is 89.12%

Merging #822 into master will not affect coverage as of 9bd8a6e

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[ghost]

Would it also be useful to have a link to the scaladoc hierarchy under "content hierarchy in http://non.github.io/cats/api/#cats.package ?

[ghost]

Also see https://github.com/non/cats/issues/95, and http://plastic-idolatry.com/erik/cats-graph.png from https://github.com/non/cats/issues/95#issuecomment-114023955

[ceedubs]

Nice! Thanks, @rklaehn.

@non I know you had previously created a diagram, but I don't think we ever got it into the site itself. Do you have any thoughts on this approach vs yours?

[ceedubs]

👍

We can always put in another diagram in the future if we want, but I think this is a great start.

[DavidGregory084]

size?

[stew]

here is an svg of this same diagram that is free of licensing restrictions: