Release v2.0.0-rc02

v2.0.0-rc02

• Added interface IIso7064PureSystemProvider implemented by all pure system providers;
• Optimized string allocations when computing check digits of validating values;
• Included license, logo and readme on Nuget packages

v2.0.0-rc01

• [BREAKING CHANGE] Reduced the number of directly target frameworks to the following:
  • .NET Standard 1.0;
  • .NET Standard 2.0;
  • .NET Framework 2.0;
  • .NET Framework 4.0;
  • .NET 5.0;
• Enabled check for nullable reference types;