Emulation thread

In Steem v4 there is a new option to run emulation in an apart thread. It was rather easy to do because Steem was well programmed - just encapsulate run() in the thread, basically - but you never know, there could be some bugs (it is "thread-safe"?... maybe not), so it's optional (on the Misc. option page). There are no designed locks (mutexes) in any case. The only parts needing attention were the reset exception (because of the longjmp) and the agendas (used in regular disk drive emulation), which had a useless (IMO) critical section.
This apart thread should make Steem more responsive.
Steem gets a tad more system resources for its supplementary thread, but it's for a good reason. One thread is busy with those pesky Windows messages, another thread runs the ST.
This should mean that input (keyboard...) is handled in almost real time, not with more than one frame delay, but maybe I'm dreaming.
Without that option, everything is handled by one single thread like before, messages are handled between frames, and emulation freezes while you use the GUI (with the funny sound loop effect).