Update docs URL.
Default to not showing mouse cursor. Closes #35.
Allow both left-button drags and right-clicks.

This requires additional logic to avoid triggering a left-button-down
event if a two-finger tap is being attempted.
Reset mouse position to 0,0 when no touches are happening.

This is to mirror the behaviour in Ren'Py on Android.
Set Ren'Py screen variant appropriately for tablet and phone.
Let user re-show keyboard by tapping.
Don't show keyboard automatically when creating a text input.
Allow special characters in path to game source directory.