Multi-targeting cross-platform validator library pointing at .netstandard 2.0 and .net framework 4.7.

Inspired by DataAnnotationsValidatorRecursive owned by @reustmd

• The recursiveness algorithm has been rewritten.

• Added cache to hold properties info by type

• Included as part of the member name

  • the zero-based index of the objects contained in enumerations

    • Child.GrandChildren[1].PropertyA

  • the key-based index of the objects contained in a enumeration of KeyValuePair<,> type

    • DataList[0][Index=1, Key="key1"]

• Improved unit tests

• Enhanced code with some handy features of the latest c# version