Simple IP Calculator sub/sup networking

The 'icalc' is versatile tool for network/system administators as well as general users (implemented in a single file pure Ruby code). Give it one of the <ip_address> <netmask> | <ip_address/prifix> | <ip_range>, e.g. <start_ipaddr-end_ipaddr> pairs, it compute rest of the things like network, broadcast, prefix, netmask, class and, or subnet charts divided by a valid divider.

ChangeLog:
* icalc.rb: wrapped some methods in module ICALC
* mdoc: added rdoc's for above module