Added ggplot continuous/discrete color/fill scales

[hrbrmstr]

Incorporates work by @noamross along with a few more examples in the scale_*_viridis functions.

I modified DESCRIPTION to add the contributors but also add Suggests and Imports dependencies.

[sjmgarnier]

@hrbrmstr I don't need to merge @noamross PR if I merge yours, correct?

[hrbrmstr]

Correct. I incorporated his stuff into this.

On Sun, Jul 19, 2015 at 5:15 PM, Simon Garnier notifications@github.com
wrote:

@hrbrmstr https://github.com/hrbrmstr I don't need to merge @noamross
https://github.com/noamross PR if I merge yours, correct?

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#4 (comment).

[sjmgarnier]

close #3