Add support for undocumented Z80 instructions

[morozov]

Currently, Skoolkit disassembles the sequence of bytes 0xED70 as DEFB $ED,$70, however, this is an undocumented Z80 instruction IN F,(C) (source). It may not be supported by all Z80 replicas but is supported by at least some emulators (e.g. Fuse).

This instruction is used by Project O.T.L.A. to implement a turbo loader:

pi_LOW  inc a
        in f,(c)
        jp po, pi_LOW

        out (c),e
pi_HIGH inc a
        in f,(c)
        jp pe, pi_HIGH

It would be nice to have these instructions supported in Skoolkit. At least for the sake of completeness.