add coveralls

Gemfile

@@ -6,6 +6,10 @@ group :docs do
   gem "maruku"
 end
 
+group :test do
+  gem "coveralls", require: false
+end
+
 platform :mri do
   gem "ruby-prof"
 end

README.md

@@ -2,6 +2,7 @@
 
 [![Build Status](https://secure.travis-ci.org/haml/haml.png?branch=master)](http://travis-ci.org/haml/haml)
 [![Code Climate](https://codeclimate.com/github/haml/haml.png)](https://codeclimate.com/github/haml/haml)
+[![Coverage Status](https://coveralls.io/repos/haml/haml/badge.png)](https://coveralls.io/r/haml/haml)
 
 Haml is a templating engine for HTML. It's designed to make it both easier and
 more pleasant to write HTML documents, by eliminating redundancy, reflecting the

test/test_helper.rb

@@ -1,3 +1,6 @@
+require 'coveralls'
+Coveralls.wear!
+
 if ENV["COVERAGE"]
   require "simplecov"
   SimpleCov.start