added math utilities

This adds
- node::util::digits2(n) which computes the number
  of digits of n in binary representation
- node::util::digits(n, base) which computes the number
  of digits of n in the „base“ system
- node::util::ipow(base, exp) which computes base^exp
added node::buffer::append_number(n, base)
added getters for the socket to http's req/res