Linear numeric classes

[utdemir]

From comment: https://github.com/tweag/linear-base/pull/217/files#r494771420

We are lacking some numeric typeclasses from base, at least:

Prelude.Real
Prelude.Integral
Prelude.Floating
Prelude.Fractional
Prelude.RealFrac
Prelude.RealFloat

We should have linear equivalent of those, with corresponding instances.

Similarly, some numeric functions in Prelude does not have linear versions either (from https://github.com/tweag/linear-base/pull/217/files#r494771588):

subtract
even
odd
gcd
lcm
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