Better support for iPhone/iPod/iPad

[tommythorn]

It's AFAICT impossible to use the iOS soft-keyboard in a way that would work
for jsnascom (trust me, I spend many hours on this).

The solution would be to autodetect iOS and provide a custom Nascom keyboard.

Another common complain is that it's slow, especially on slightly older hardware.
This is a know problem and can be fixed. jslinux proved that javascript, even
on an iPhone, is plenty fast for emulation, and certainly a 4 MHz Z80 should be
no problem.