Strong name signing and more

[spreedated]

Adressing #88

• Swtiched to net6, since it's LTS and 5.0 is no longer supported
• The projects are now strong named.
• Fixed error of index out of bounds when InputStream was null (including fallback), on extension ParseFormUrlEncodedData()
• Added mocking to unitests
• Added several test on methods I altered
• linted a lot of code, used LINQ on many parts, made public members to properties, from originally fields, used null checks when some code paths may get into null object to prevent null-ref-exception, etc.

Note: I'm not used to xunit nor shoudly, I prefer nunit - so feel free to rewrite the tests to conform the pattern.

[scottoffen]

These look great so far. I'd like to continue to target 5.0 in this version for those that have not yet upgraded. I'll remove that when I update the major version to 6.0.

[spreedated]

You can still do a legacy support by simply adding net 5.0 to the FrameWorks tag:

From:
<TargetFrameworks>netstandard2.0;netstandard2.1;net6.0</TargetFrameworks>

To:
<TargetFrameworks>netstandard2.0;netstandard2.1;net6.0;net5.0</TargetFrameworks>

[scottoffen]

I appreciate your desire to contribute! Please refer to the contribution guidelines, specifically the item:

• Pull Requests Make sure all of your commits are atomic (one feature per commit)

I'd like to add some of the changes, but not others, and having everything wrapped up in this PR as an all-or-nothing approach leaves me no option to only allow some of the changes. Feel free to resubmit each change or group of changes as an atomic PR.