#96 Add support for DISCiPLE inhibit button
Crisis happened to summarise the DISCiPLE inhibit behaviour on WoS:
Disciple is invoked /inhibited with an OUT command. its in the manual www.worldofspectrum.org/pub/sinclair/hardware-info/DISCiPLEInterface_UserManual.pdf
3. Press the Inhibit Button once, so that it is locked in; this gives you the capability of switching off the Disciple's operating system. To actually turn off the system, enter OUT 31,0. You can now no longer use your disk drive (although the Disciple's printer and joystick ports remain active), but you will probably be able to use your peripheral. If now, for example, you entered CAT 1 with Interface 1 and a Microdrive attached behind the Disciple, you would display the Microdrive's directory, not the Disciple's.
4. When you wish to use the Disciple's disk drive again, you can either press the Inhibit Button again (so that it is no longer latched in), or you can enter OUT 31,16. You can then continue to use the Disciple in the normal way. So, if you have loaded a program from Microdrive into the computer, you could now save it to disk, with either the SAVE command, or with the Snapshot Button. (Programmer's note: You can use OUT 31,0 and OUT 31,16 in your programs to turn the Disciple's DOS on and off. See List 1 in Appendix A.)
Fuse has a disciple_inhibited flag to track whether the inhibit bit in the control port has been set but no emulation of the inhibit button itself. The flag also doesn't have the effect of locking out the disk ports/functionality and needs to be added.
