* started adding network management functionality (ipam.lisp, inc/sections/manage-networks.lisp)
* the use of "network" when describing blocks of special use ipv4 addresses has been replaced with "block"
* blocks are now applicable - they can be managed
* added functions get-applicable-blocks, host-in-ipv4-applicable-block-p, ipv4-network-overlaps-p and allocate-network to inc/database.lisp
* added macros invalid-mask-handler and ipv4-validator handler to be used in inc/section/calculator.lisp and inc/section/manage-networks.lisp
* changed use of "subnet mask" to "network mask"
* added function is-network-address-p to inc/functions.lisp