adding iterators; isolating VERSION file

[tilo]

@knu @hsbt Changes in this PR:

• isolates the VERSION file

• adds iterators:

  • .each : all addresses in a given range
  • .each_host : all usable host addresses in a given range

• adds size helpers:

  • .ip_range_size : number of all addresses in given range
  • .usable_hosts_size : number of usable host addresses in given range

[tilo]

@knu can this be merged?

[hsbt]

Can you separate isolate version constant and iterators and others?