Add converter from image/color.Color to tcell.Color

[spenserblack]

Resolves #450

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@299cb41). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #456   +/-   ##
=========================================
  Coverage          ?   17.07%           
=========================================
  Files             ?       20           
  Lines             ?     1388           
  Branches          ?        0           
=========================================
  Hits              ?      237           
  Misses            ?     1137           
  Partials          ?       14           

Impacted Files	Coverage Δ
color.go	86.20% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 299cb41...1556756. Read the comment docs.

[gdamore]

I was a bit hesitant about this at first, but it seems kind of ok. I don't think it brings huge value, but as image/color is part of the standard library I guess it's worth doing. I looked a bit more closely at image/color and can say that I would not recommend using it's matching, which is the naive Euclidean shortest path match. (Otherwise I might be tempted to use it for the color handling internally. Alas, it's not up to it.)

[spenserblack]

Thanks for merging!

I don't think it brings huge value

I'm currently working on a project to view images in the terminal, and this small function can help a lot. Not a huge value, but I think rendering images in terminal is common enough (e.g. termui's image widget) for this library to provide this utility.