math: add more constants

~* Golden ratio, sqrt(2 and 3), ln(2), ...~
A lot of constants have already been implemented by @kelanialiyu in #15. Still, there's always room for more, which is why I'm leaving this issue open for now.

They can be implemented like `pi` and `e` using functions for now (although this is very inefficient and we should figure out a better solution soon).

Start by locating the existing pi and e functions, which the issue identifies as the current implementation pattern. Determine the exact additional constants to include and how they should be exposed; the work is done when those constants are available through the language in the same way as pi and e.

Written by the indexing model from the issue text.