Drop Support for Older .NET Versions

[WalkerCodeRanger]

As of Semver v2.1.0, it will ship with DLLs targeting .NET 4.5.2, .NET Standard 1.1, and .NET Standard 2.0. However, this includes support for versions with are no longer supported by Microsoft. At some point, it is likely to become a problem to support those versions. This also limits which version of the C# language we can use. There may be features in newer versions of C# that would be beneficial to use. When the next major release occurs, we should drop support for some frameworks. We will have to decide at that point which ones it makes sense to drop support for.

MS Supported Version

• Microsoft .NET Framework
• Microsoft .NET and .NET Core

From what I can tell, .NET Standard doesn't have a separate support lifecycle from the individual frameworks they support. However, MS is already saying that it is "recommend you target .NET Standard 2.0, unless you need to support an earlier version."

For reference, the old .NET standard support chart which is easier to read is reproduced here. Also, here is an article on Demystifying Microsoft .NET Long-term Support (LTS).

[WalkerCodeRanger]

Looking at the .NET Standard supported plaforms it looks like .NET Standard 2.0 is supported on all versions that still have suport. It appears Xamerin drops support for old versions very quickly. I was unable to find anything on Mono versions long term support.

[WalkerCodeRanger]

Support for target frameworks before .NET Standard 2.0 has been dropped. The reasons for targeting .NET Standard 2.0 & 2.1 and .NET 5 have been documented in FRAMEWORK_SUPPORT.md.

Thus, this has been fixed on master and will be included in v3.0.0