Replaces the free-standing functions in f32, &c.

[auroranockert]

The free-standing functions in f32, f64, i8, i16, i32, i64, u8, u16,
u32, u64, float, int, and uint are replaced with generic functions in
num instead.

This means that instead of having to know everywhere what the type is, like

f64::sin(x)

You can simply write code that uses the type-generic versions in num instead, this works for all types that implement the corresponding trait in num.

num::sin(x)

Note 1: If you were previously using any of those functions, just replace them
with the corresponding function with the same name in num.

Note 2: If you were using a function that corresponds to an operator, use the
operator instead.

[brendanzab]

looks good!

[Casorati]

This looks nice, thanks for all the work.
I'm reviewing the code. I have found one thing I don't like, that is
#[inline(always)] pub fn abs<T: Signed>(value: T) -> T { value.abs() }
I don't like it because,

1. abs can as well be defined for unsigned number as the identity.
2. abs is usually understood to be the L2 norm and is defined for normed vector space and we probably want to define it for complex numbers although they are not "Signed".

[brendanzab]

@Casorati would you be able to move this discussion to #4819? This is where most of the discussion about the numeric traits has been going on.