Wrappers for [Initialize/Update]ProcThreadAttributeList & CreateProcess

[rasta-mouse]

Initial draft for providing wrappers for InitializeProcThreadAttributeList, InitializeProcThreadAttributeList and CreateProcess. DeleteProcThreadAttributeList to follow.

Feedback welcome - particularly interested in your option on issues like:
https://github.com/rasta-mouse/DInvoke/blob/dev/DInvoke/DInvoke/DynamicInvoke/Win32.cs#L117-L120

I've currently abstracted SECURITY_ATTRIBUTES away from the user, as I feel most use cases would not have a need to change them. But should we not do that? Should they be optional overloads?

Changes can be tested with the following:

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

using DInvoke.DynamicInvoke;
using Data = DInvoke.Data;

namespace TestApp
{
    class Program
    {
        static void Main(string[] args)
        {
            var si = new Data.Win32.ProcessThreadsAPI._STARTUPINFOEX();
            si.StartupInfo.cb = (uint)Marshal.SizeOf(si);
            si.StartupInfo.dwFlags = (uint)Data.Win32.ProcessThreadsAPI.STARTF.STARTF_USESHOWWINDOW;

            var lpValue = Marshal.AllocHGlobal(IntPtr.Size);

            var lpSize = IntPtr.Zero;

            var success = Win32.InitializeProcThreadAttributeList(
                IntPtr.Zero,
                2,
                ref lpSize);

            si.lpAttributeList = Marshal.AllocHGlobal(lpSize);

            success = Win32.InitializeProcThreadAttributeList(
                si.lpAttributeList,
                2,
                ref lpSize);

            if (Is64Bit)
            {
                Marshal.WriteIntPtr(lpValue, new IntPtr(0x100000000000));
            }
            else
            {
                Marshal.WriteIntPtr(lpValue, new IntPtr(unchecked((uint)0x100000000000)));
            }

            success = Win32.UpdateProcThreadAttribute(
                si.lpAttributeList,
                (IntPtr)0x20007,
                lpValue);

            var hParent = Process.GetProcessesByName("explorer")[0].Handle;
            lpValue = Marshal.AllocHGlobal(IntPtr.Size);
            Marshal.WriteIntPtr(lpValue, hParent);

            success = Win32.UpdateProcThreadAttribute(
                si.lpAttributeList,
                (IntPtr)0x00020000,
                lpValue);

            success = Win32.CreateProcess(
                null,
                "notepad",
                0x00080000,
                null,
                ref si,
                out Data.Win32.ProcessThreadsAPI._PROCESS_INFORMATION pi);
        }

        static bool Is64Bit
        {
            get
            {
                return IntPtr.Size == 8;
            }
        }
    }
}