Add sourceMap comment to asset_hash and hash .map files by default

middleman-core/fixtures/asset-hash-source-map/lib/middleware.rb

@@ -0,0 +1,16 @@
+class Middleware
+  def initialize(app)
+    @app = app
+  end
+
+  def call(env)
+    status, headers, response = @app.call(env)
+    body = ''
+    response.each {|part| body += part }
+    if (env["PATH_INFO"] =~ /css$/)
+      body += "\n/* Added by Rack filter */"
+      status, headers, response = Rack::Response.new(body, status, headers).finish
+    end
+    [status, headers, response]
+  end
+end