Add .DW assembly instruction

[MalteT]

The .DW instruction was never really implemented, due to the fact, that it is the only instruction working with words. Since the manuals do not state the endianness that is used to store the defined two-byte words, I'll assume BigEndian until I can verify that.

[MalteT]

This is basically done, but I'll need to verify the endianness before I'll close this.