Add command filtering and mute title screen replays

(Closes #6)
Fix Last.nbr being created with the wrong path
Update install.txt

(Closes #32)
Add two sentences on MinGW and Fedora
Explain that ENABLE_NLS is enabled by default
Restrict cheat activation to letter keys

(Closes #36)
Hide cursor during flyby, stroke and roll states.

Also handle entering/leaving pause from flyby and roll.