In-language implementation of Show BitsN

They are printed as unsigned hexadecimal integers. There's no `0x`
prefix.
Make it compile, and use a List instead of a Vect

- It was necessary to add the new file lib/Prelude/Bits.idr to
  lib/base.ipkg.

- In lib/Prelude/Chars.idr, use a List instead of a Vect - no need to
  know the size.
Fix imports and make hexVect local

It *should* compile now
Merge branch 'show-bits-in-language' of https://github.com/reynir/Idris-dev into reynir-show-bits-in-language