Add color scheme previews

[ikirill]

It's kind of tedious to have to select a colour scheme going by name only, so I made previews.

I could not find out how to make SVG images display properly in github's markdown, so I had to add PNG images.

Thanks for transcribing the colour schemes, they are really quite nice.

[timothyrenner]

Wow, this looks great! Thanks for doing this!

You might be able to use an HTML embed tag for the svg, but I've got no problem with the PNGs.

[ikirill]

You're welcome, I use these in my visualization work. Have you thought of publishing ColorBrewer.jl like this: http://docs.julialang.org/en/latest/manual/packages/#publishing-your-package
Also, it might be worth pinging JuliaLang/Color.jl to mention this package in their readme, in a related-work kind of way, as another source of good colour schemes.

I noticed that YlOrRd is 8, not 9, elements long (the preview image is short, too). This is either a documentation bug, or the 9-long YlOrRd is missing from the json data.

[timothyrenner]

Thanks for pinging Color.jl and pointing out the bug. I'll open an issue and look into it.