Added hex color conversion

[jsheely]

Solves issue #1354

I'm not sure if this is desired but seemed like an easy quality of life feature to allow hex to rgb for creating colors.

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Please upvote 👍 this pull request if you are interested in it.

[patriksvensson]

• The constructor only tests the happy path.
• I think public static Color.FromHex(string hex) would be a more desirable approach here from an API perspective.
• All errors will need to be resolved.

[nils-a]

• I think public static Color.FromHex(string hex) would be a more desirable approach here from an API perspective.

I'd vote for a combination of public static Color ParseHex(string hex) and public static bool TryParseHex(string hex, out Color color)

[patriksvensson]

We use "ToHex" so "FromHex" and "TryFromHex" is more consistent API wise

[FrankRay78]

It looks like hex[2..4] is not supported in netstandard 2.0

[FrankRay78]

Unfortunately, the build still breaks @jsheely - see the build log above, looks like simple char/string conversion error. Want to update and push again?

[FrankRay78]

Thank you @jsheely, if no one else gets to it first, I'll review (and hopefully merge) your PR this week.

[FrankRay78]

Dear @patriksvensson, I have rebased this branch, implemented full unit test coverage for both happy and unhappy paths, and ensured the failure to parse an invalid colour raises a FormatException with (what seems to me) to be a reasonable message.

I think it's suitable for merging, please re-review when you can.