Add guid type to edl parser / codegen

[bbonaby]

The guid type can be easily added to the edl parser as type:

guid_t

the corresponding flatbuffer schema can be:

struct guid_t 
{
  Data1: uint32;
  Data2: uint16;
  Data3: uint16;
  Data4: [uint8: 8];
}

this is essentially the same definition as the GUID type in the windows guiddef.h header in 64 bit architectures. The current codegen would generate this as:

struct guid_t 
{
  std::uint32_t Data1;
  std::uint16_t Data2;
  std::uint16_t Data3;
  std::array<uint8_t, 8>  Data4;
}

although the memory layout is essentially the same as the windows GUID type we can add To/From conversion functions.