add to_base function

[Maxxen]

Follows the excel semantics, with the slight deviation that the optional ”min_length” parameter has an upper limit on 64 digits. This allows us to stack allocate the result string and still pad enough zeroes to fit an entire 64 bit int in base 2.

[carlopi]

Cool, couple of notes:

• using lower case letters seems somehow more usual, but I guess one can the lowering in another pass.
• what's the semantic with negative numbers as input?

[Maxxen]

Google sheets uses uppercase, so thats what i testef with.

Good catch on negative bumbers, idk, ill check tomorrow

[Maxxen]

Excel doesn't allow negative input numbers, so I've changed the implementation so that we check for it as well and throw invalidinput when detected.

[Mytherin]

Thanks for the PR! LGTM - some comments

[Mytherin]

Thanks!