Use floating point numbers instead of fixed point numbers

Use floating point numbers instead of fixed point numbers

Fixed point numbers can easily overflow, and double to fixed point
conversion is lossy. Use floating point (double) where fixed point
numbers where previously used and remove the li_fixed_t type.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>