Provide handy constants

[rawhuul]

Hi, as the library is geared towards mathematical computation, it would be great if it included constants such as: Archimedes' constant π, Euler's number e, The golden ratio φ, Euler–Mascheroni constant γ, Conway's constant λ, The imaginary unit i, etc.

[Tony-Samuels]

Definitely can't do i. You'll need a complex numbers library for that. The rest are doable although they can be converted from any other source with constants as floats or strings.