Preserve match_data in rules

[fatkodima]

Closes #141

Example of usage (from the issue):

rule /^members/(?<email>.*)/\d{2}-(?<step>\w+).timestamp$/ do |t|
  email = t.match_data[:email]
  step  = t.match_data[:step]
  # ...
end

cc/ @avdi

[avdi]

Cool!!!