Add feature describing expected serialization of docstrings

This is intended to help reproduce and diagnose
cucumber/cucumber-ruby#1183.

features/docstring.feature

@@ -0,0 +1,39 @@
+Feature: Wire protocol docstrings
+
+  In order to use docstrings as arguments to step definitions, we send them as
+  an additional argument after the arguments extracted by the wire server.
+
+  Background:
+    Given a file named "features/step_definitions/some_remote_place.wire" with:
+      """
+      host: localhost
+      port: 54321
+
+      """
+
+  Scenario: Run a scenario
+    Given a file named "features/wired.feature" with:
+      """
+      Feature: High strung
+        Scenario: Wired
+          Given we're all wired
+            \"\"\"
+            to want more
+            \"\"\"
+      """
+    And there is a wire server running on port 54321 which understands the following protocol:
+      | request                                              | response                            |
+      | ["step_matches",{"name_to_match":"we're all wired"}] | ["success",[{"id":"1", "args":[]}]] |
+      | ["begin_scenario"]                                   | ["success"]                         |
+      | ["invoke",{"id":"1","args":["to want more"]}]        | ["success"]                         |
+      | ["end_scenario"]                                     | ["success"]                         |
+    When I run `cucumber -f progress`
+    Then the stderr should not contain anything
+    And it should pass with:
+      """
+      .
+
+      1 scenario (1 passed)
+      1 step (1 passed)
+
+      """