Add new Color parsing methods.

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

• Adds Color.TryParse
• Adds Color.Parse
• Adds Color.TryParseHex
• Renames Color.FromHex to Color.ParseHex
• Adds Rgba32.TryParseHex
• Renames Rgba32.FromHex to Rgba32.ParseHex

Color.TryParse and Color.Parse recognize both color names and hexadecimal representation as per CSS4 specification in ordinal casing. Fix #1103

I haven't added Rgba32.TryParse and Rgba32.Parse as I'm very tempted to drop the Rgba32 named colors. I'd much rather channel color creation through the Color struct only.

Please let me know if you agree that this is the best course of action.

EDIT. I went ahead and deleted them. Much happier now.

[codecov]

Codecov Report

Merging #1104 into master will increase coverage by 0.69%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1104      +/-   ##
==========================================
+ Coverage   81.53%   82.22%   +0.69%     
==========================================
  Files         704      702       -2     
  Lines       29384    29159     -225     
  Branches     3290     3296       +6     
==========================================
+ Hits        23957    23977      +20     
+ Misses       4734     4491     -243     
+ Partials      693      691       -2

Flag	Coverage Δ
#unittests	82.22% <100%> (+0.69%)	⬆️

Impacted Files	Coverage Δ
...rp/PixelFormats/PixelImplementations/RgbaVector.cs	93.18% <100%> (ø)	⬆️
src/ImageSharp/Color/Color.WernerPalette.cs	100% <100%> (ø)	⬆️
src/ImageSharp/Color/Color.NamedColors.cs	100% <100%> (ø)	⬆️
...eSharp/PixelFormats/PixelImplementations/Rgba32.cs	97.93% <100%> (+3%)	⬆️
src/ImageSharp/Color/Color.cs	95.74% <100%> (+1.99%)	⬆️

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[JimBobSquarePants]

@SixLabors/core Any objections to this. I'll add it tonight otherwise.

[brianpopow]

@SixLabors/core Any objections to this. I'll add it tonight otherwise.

i have looked trough the changes. Looks good to me, i think it can be merged.

[jespersh]

Is this the commit that broke examples that use like?:

image.Mutate(x => x.BackgroundColor(Rgba32.White));

I suppose the replacement is just using Color.White instead?

[JimBobSquarePants]

There’s nothing broken, this is by design. Color is the correct pixel agnostic way to declare colors.

[jespersh]

I didn't say it was broken, I said it broke the examples 😄

[JimBobSquarePants]

Which examples are broken? I’ll update if we own them.

[jespersh]

I followed this path to here:
https://stackoverflow.com/a/60642706
#355 (comment)

Thanks for this library.

[JimBobSquarePants]

@jespersh no worries! yeah, that's all out of date. We've got API docs https://docs.sixlabors.com/ that will be much more useful.