Upgrade .netstandard to 2.0

[shargon]

Currently we have this framework:

<TargetFrameworks>netstandard1.6;net461</TargetFrameworks>

In order to unify the projects i think that we should define it as:

<TargetFramework>netcoreapp2.2</TargetFramework>

[erikzhang]

We need to keep it as .NET Standard project for compatibility.

[shargon]

I want to use some reflection methods and i have problems

I think that we can use Attributes for make cleaner the new PR

private static OperandBaseAttribute[] operandCache = new OperandBaseAttribute[byte.MaxValue];

        static Instruction()
        {
            foreach (OpCode op in Enum.GetValues(typeof(OpCode)))
            {
                operandCache[(byte)op] = op.GetAttributeOfType<OperandBaseAttribute>();
            }
        }

internal Instruction(byte[] script, int ip)
        {
            this.OpCode = (OpCode)script[ip++];
            this.Size = 1;

            var parser = operandCache[(byte)this.OpCode];

            if (parser != null)
            {
                Operand = parser.ReadOperand(script, ref ip, ref this.Size);
            }
            else
            {
                Operand = new byte[0];
            }
        }

[erikzhang]

You can upgrade it to .NET Standard 2.0

[erikzhang]

Also, I don't think reflection will be faster than switch.

[shargon]

reflection is slower, but should be cached in a static way

[erikzhang]

The difficulty of using Attributes on OpCode is the values between PUSHBYTES1 and PUSHBYTES75.

[shargon]

I added these enum values :P, do you like it? xD

[erikzhang]

@shargon I studied it and found no good way to use Attributes to cache size information. The main problem is the values between PUSHBYTES1 and PUSHBYTES75. If you have any good ways, commit them directly to this PR.

[erikzhang]

I added these enum values :P, do you like it? xD

No, this is too cumbersome. . .

[erikzhang]

Wait, if you didn't use reflection, there is no need to upgrade .NET Standard to 2.0

[shargon]

Ok, i will made a PR with this and reflection, and we can evaluate if is better or not

[erikzhang]

Can you approve #102, and make a new PR with reflection?