Macro define_float_funcs

macro_rules! define_float_funcs {
    ($(
        fn $name:ident(self $(,$arg:ident: $arg_ty:ty)*) -> $ret:ty
        => $lname:ident/$lfname:ident;
    )+) => { ... };
}

Defines a trait that chooses between libstd or libm implementations of float methods.

Some methods will eventually became available in core by core_float_math