Added short_domains argument to initialize.

[rhiroe]

close: #186

Added short_domains argument to initialize method to accept Boolean.
This is false by default, and if you set it to true, Rinku::AUTOLINK_SHORT_DOMAINS will be set to the flags argument of Rinku.auto_link.
This allows you to autolink short domains.

AutoHtml::Link.new(short_domains: true).call('http://localhost:3000')
#=> "<a href=\"http://localhost:3000\">http://localhost:3000</a>"

The reason for using Boolean is to isolate the behavior for each environment.

AutoHtml::Link.new(short_domains: !Rails.env.production?)

There is no change to the default behavior, so existing projects that use this gem will not be affected.

AutoHtml::Link.new.call('http://localhost:3000')
#=> "http://localhost:3000"

[dejan]

@rhiroe thanks!