Restrict clamp01 to gray & RGB

[timholy]

The 0-to-1 colorscale does not have meaning for colors like HSV,
so supporting arbitrary colorants seems wrong.

I noticed this while working on JuliaImages/MultiChannelColors.jl#4. We might not want to merge this until we decide to make a push for the next breaking release.

[timholy]

Have you noticed the CI failure previously? It happens on master too. I haven't delved deeply to see what changed it, but from a quick debug it has to do with using the typeinfo in display, i.e., https://github.com/JuliaGraphics/ColorTypes.jl/blob/b8ed378531f1445ed2402a00d49ecbf64ce5a0fc/src/show.jl#L11-L18. What puzzles me is that this isn't new. Maybe there was some dependency change?

I think the new way of printing is nicer so wondering if we should change the docstring, but it would be nice to know what dependency changed so we can add it to the [compat].

[johnnychen94]

It's because you've made a ColorTypes release v0.11.1 4 days ago and shipped every commit before that JuliaGraphics/ColorTypes.jl@b8ed378#comments 😆

I guess @kimikage planned a bigger release v0.12 or so. BTW, I'm wondering what happened to him; haven't seen him active for quite a long time. Hope he's still okay.

[timholy]

Oh shoot. I didn't check how much was on master, big mistake.

I will try to fix this. I think the best plan is to fork a release 0.11 branch, backport my recent commit, and release 0.11.2. Reasonable?

[codecov]

Codecov Report

Merging #181 (ad9bcc8) into master (9e64fec) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #181   +/-   ##
=======================================
  Coverage   62.60%   62.60%           
=======================================
  Files          10       10           
  Lines         583      583           
=======================================
  Hits          365      365           
  Misses        218      218           

Impacted Files	Coverage Δ
src/map.jl	100.00% <100.00%> (ø)

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