Support .vtfixup directives in assembly manifest

[MSDN.WhiteKnight]

C++/CLI assemblies contain VTable fixups declared like this:

.vtfixup [1] int32 retainappdomain at D_0000E000 // 06000001
.vtfixup [1] int32 retainappdomain at D_0000E00C // 06000029
.vtfixup [1] int32 retainappdomain at D_0000E010 // 06000004
.vtfixup [1] int32 retainappdomain at D_0000E014 // 06000005
.vtfixup [1] int32 retainappdomain at D_0000E018 // 06000006

ECMA-335 II.15.5.1 - Method transition thunks

Related to #69