Raise ArgumentError if IP address is nil

Fix <=> for IPv4 and IPv6.

It removes below ruby's warning when running test.

* "(...) interpreted as grouped expression"

It removes below ruby's warning.

* "mismatched indentations"

Integer Unification for Ruby 2.4.0+

Add IPv6#link_local?

Travis CI fix

See https://github.com/codeclimate/ruby-test-reporter/blob/master/README.md#upgrading-from-pre-10-versions for details.

Add Travis, CodeClimate, and Jeweler

…and gem install stuff in travis

70 contributing md

# Conflicts:
#	.gitignore

add minitest to development group in Gemfile