rename unreadable variables, 'port1/port2' to '[begin_]port/end_port'
add parser.rb and move 'racc' to development group in Gemfile

* parser.rb is generated from parser.ry by racc as distributable code using -E(embedded) option.
  so that, racc package do not needed for runtime. it will be needed only when develop parser.
* refactorint: hash key existance check