Add unit tests and multi-target for maximum compatibility

[joelverhagen]

Hey J. Daniel Smith,

I found this library the StackOverflow question referenced in your source and was happy to see a C# implementation.

What do you think about making it a NuGet package? This could ease re-use. A description of my changes is enumerated below but I added some start metadata for this purpose.

I made a couple of tweaks to improve cross-platform usage.

Question for you: is this code public domain, or is it MIT? I see the LICENSE file at the root of the repo says MIT but some comments and text say public domain, so I'm not sure. Right now, I have the .nupkg license info set to MIT to be on the safe side.

I'm happy to publish it to NuGet.org and add you as an owner, or you can do it if you'd like sole ownership -- whatever works best for you.

Also, I'm happy to adjust this PR to meet your requirements. My primary goal is having it on NuGet but I figured I'd polish a couple of other things while I was in there.

Changes:

• Add unit tests
• Change from regex to simple parsing to allow net40 compat
• Mutli-target to netstandard1.0 and net40
• Add NuGet package metadata
• Add GitHub Actions definition for build and test
• Rename directories and files to be consistently "Base16k"

[JDanielSmith]

Please feel free to make any tweaks you feel are necessary to make this easier to use.

The license in the source code is what matters; I think GitHub defaults to a MIT license, so that's what I used.

Thanks for the feedback and changes! :-)

Dan