Support .vtentry directive

[MSDN.WhiteKnight]

Example C++/CLI program:

using namespace System;

public class A {
    int _x;
    public: A(int x) { this->_x = x; }
};

int main(array<System::String ^> ^args)
{
    A a(1);
	Console::ReadKey();
    return 0;
}

Expected disassembler output:

.method assembly static valuetype A* modopt([mscorlib]System.Runtime.CompilerServices.CallConvThiscall)
        'A.{ctor}'(valuetype A* modopt([mscorlib]System.Runtime.CompilerServices.IsConst) modopt([mscorlib]System.Runtime.CompilerServices.IsConst) A_0,
                   int32 x) cil managed
{
  .vtentry 1 : 1
  //...
}

The VTable data is stored in the location pointed int the CLI Header (ECMA 335 II.25.3.3). Code to get vtable data:

PEReader pr;
//...
int vt_rva = pr.PEHeaders.CorHeader.VtableFixupsDirectory.RelativeVirtualAddress;
var vt_data=pr.GetSectionData(vt_rva).GetContent();