Add architecture for x86 real mode.

[i509VCB]

A new x86_16 architecture is added to allow decoding instructions in real mode. This is useful especially for relative jumps where the jump depends on the instruction.

Fixes #21

This is untested since it appears there is no go.mod in the project for me to test locally and the build info is quite empty.

[i509VCB]

I guess this has sat for 2 years... Just a quick poke.