betterer short-ID generator

[buhman]

rfc3986:

2.3.  Unreserved Characters

   Characters that are allowed in a URI but do not have a reserved
   purpose are called unreserved.  These include uppercase and lowercase
   letters, decimal digits, hyphen, period, underscore, and tilde.

      unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

These will be used in our custom base66 encoder. Ideally we'd also use a simple replacement cipher or similar so we get 'cool-looking' urls instead of: '001', '002', etc.., we'd get 2xz and 8y~ and similar.

This would also remove the dependency on bitstring.