Remove BouncyCastle dependency to use System.Security.Cryptography

[nanspanico]

Remove BouncyCastle dependency to use System.Security.Cryptography. Add .net48 support Remove .netstandard1.1 et .netstandard2.0 don't support all crypto methods

[coryjthompson]

Hi,

Thanks for this work.

I look at merging this in however it uses a few APIs that are only available on windows.

I would love to replace them with cross platform alternatives once i get some time to get this merged in.

[SitecHQ]

Remove BouncyCastle dependency to use System.Security.Cryptography. Add .net48 support Remove .netstandard1.1 et .netstandard2.0 don't support all crypto methods

Looks good! Could you please remove .net48 and do the cryptography in .net core only