CPP11 — Missing constructor for Fixed

Summary: Type Fixed has constructors for LongDouble and int. This causes
a few initialization problems. For example:

Fixed<8,2> x = 6.75;
Fixed<8,2> y = 10L;
Fixed<8,2> z = 10U;

None of these will compile because of the ambiguity as to whether to use
the int or the LongDouble constructor.

I think Fixed will need additional constructors to allow initialization
from float, double, long and unsigned values.