Add rdoc task to activemodel. [#156 state:resolved]

Signed-off-by: NPratik Naik <pratiknaik@gmail.com>

activemodel/Rakefile

 #!/usr/bin/env ruby
 $LOAD_PATH << File.join(File.dirname(__FILE__), 'vendor', 'rspec', 'lib')
 require 'rake'
-require 'spec/rake/spectask'
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+require 'spec/rake/spectask'
+require 'rake/rdoctask'
+
+# Generate the RDoc documentation
+Rake::RDocTask.new { |rdoc|
+  rdoc.rdoc_dir = 'doc'
+  rdoc.title    = "Active Model"
+  rdoc.options << '--line-numbers' << '--inline-source' << '-A cattr_accessor=object'
+  rdoc.options << '--charset' << 'utf-8'
+  rdoc.template = "#{ENV['template']}.rb" if ENV['template']
+  rdoc.rdoc_files.include('README', 'CHANGES')
+  rdoc.rdoc_files.include('lib/**/*.rb')
+}
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