all-your-base: Add exercise, and deprecate binary

[ee7]

Reference:
exercism/problem-specifications/exercises/all-your-base

Implementation details:
Similar to other tracks (e.g. Haskell and Rust), the function's arguments are ordered differently than in the canonical data. The new order is more idiomatic Nim, and it allows clean use of Nim's method call syntax: [1, 0, 1].convert(2, 10).

I don't have strong opinions about using array rather than seq for the input digits, but this could be an opportunity for Nim students to practise using openArray.

Deprecation:
The all-your-base exercise replaces the binary exercise, which will be officially deprecated soon.