Implement lexer for Crystal

Take from rouge-ruby/rouge#441

.travis.yml

@@ -1,5 +1,19 @@
 sudo: false
+dist: trusty
 language: ruby
 rvm:
-  - 2.5.1
-before_install: gem install bundler -v 1.16.2
+  - "2.0"
+  - "2.1"
+  - "2.2"
+  - "2.3"
+  - "2.4"
+  - "2.5"
+
+cache:
+  bundler: true
+bundler_args: --without development
+before_install:
+  - gem install bundler
+  - gem update --system
+script:
+  - bundle exec rake

README.md

@@ -1,8 +1,8 @@
 # Rouge::Lexers::Crystal
 
-Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file `lib/rouge/lexers/crystal`. To experiment with that code, run `bin/console` for an interactive prompt.
+[Crystal](https://crystal-lang.org) lexer for [rouge](http://rouge.jneen.net/).
 
-TODO: Delete this and the text above, and describe your gem
+This gem exists because rouge lacks support for the Crystal language. These PRs are pending: [441](/~https://github.com/jneen/rouge/pull/441) and [863](/~https://github.com/jneen/rouge/pull/863).
 
 ## Installation
 
@@ -22,7 +22,8 @@ Or install it yourself as:
 
 ## Usage
 
-TODO: Write usage instructions here
+See rouge's [README](/~https://github.com/jneen/rouge/blob/master/README.md) for the full description.
+
 
 ## Development
 

Rakefile

@@ -2,9 +2,9 @@ require "bundler/gem_tasks"
 require "rake/testtask"
 
 Rake::TestTask.new(:test) do |t|
-  t.libs << "test"
+  t.libs << "spec"
   t.libs << "lib"
-  t.test_files = FileList["test/**/*_test.rb"]
+  t.test_files = FileList["spec/**/*_spec.rb"]
 end
 
 task :default => :test

lib/rouge-lexers-crystal.rb

@@ -0,0 +1 @@
+require "rouge/lexers/crystal"