4.4.0

• New polyfills for the .NET Framework 4.5 and .NET Standard 2.0:

    StringBuilder AppendJoin(this StringBuilder, char, params string?[]);
    StringBuilder AppendJoin(this StringBuilder, char, params object?[]);
    StringBuilder AppendJoin<T>(this StringBuilder, char, IEnumerable<T>);
    StringBuilder AppendJoin(this StringBuilder, string?, params string?[]);
    StringBuilder AppendJoin(this StringBuilder, string?, params object?[]);
    StringBuilder AppendJoin<T>(this StringBuilder, string?, IEnumerable<T>);