Improved 'vars_prompt' syntax to support prompt text and (non-)private input

An example of the new syntax:

vars_prompt:
 - name: 'secret_variable_name"
   prompt: "Enter secret value: "
   private: "yes"
 - name: "nonsecret_variable_name"
   prompt: "Enter non-secret value: "
   private: "no"

examples/playbooks/prompts.yml

@@ -12,22 +12,35 @@
      this_is_a_regular_var: 'moo'
      so_is_this: 'quack'
 
-# prompted variables are a list of variable names and a description
-# that will be presented to the user.
-#
 # alternatively, they can ALSO be passed in from the outside:
 #    ansible-playbook foo.yml --extra-vars="foo=100 bar=101"
 # or through external inventory scripts (see online API docs)
 
+# prompted variables are a list of variable names and a description
+# that will be presented to the user, or a list of variable dictionaries
+# with the following accepted keys / value types: 
+#    'name' / text
+#    'prompt' / text (optional)
+#    'private' / boolean (optional)
+
+# prompted variables as key/value pairs:
   vars_prompt:
      release_version: "product release version"
 
-  tasks:
+# prompted variables as a list of variable dictionaries:
+#  vars_prompt:
+#    - name: "some_password"
+#      prompt: "Enter password: "
+#      private: True
+#    - name: "release_version"
+#      prompt: "Product release version: "
+#      private: False
 
 # this is just a simple example to show that vars_prompt works, but
 # you might ask for a tag to use with the git module or perhaps
 # a package version to use with the yum module.
 
+  tasks:
   - name: imagine this did something interesting with $release_version
     action: shell echo foo >> /tmp/$release_version-$alpha