improve asynchonous publishing performance (fix #373)
roscpp: Adding AsyncSpinner::canStart to check if a spinner can be started
add warning when queue_size is omitted for rospy publisher (#346)
roslaunch: Adding 'doc' attribute to roslaunch <arg> tags

* This adds a 'doc' attribute to the roslaunch <arg> tag
* This tag is read in and stored in the resolve_dict under 'arg_doc'
* The keys in resolve_dict['arg_doc'] are the argument names, and the
  values are tuples where the first element is None or the doc string,
  and the second element is None or the default value.
* The arg_dump.get_args function still returns a dict, so the return
  value's keys can still be used for a list of arg names.
* A unit test has been added to test_roslaunch/test/roslaunch.test which
  loads the ros_args.launch launchfile and compares the output of
  arg_dump.get_args to the expected output.
Merge pull request #379 from jhu-lcsr-forks/roslaunch-arg-doc

Adding 'doc' attribute to roslaunch <arg> tags
Merge pull request #374 from ros/rospy_async_publish_performance

improve asynchonous publishing performance
Merge pull request #372 from ros/rospy_warn_publisher_queue_size

add warning when queue_size is omitted for rospy publisher
Allow for custom error handlers for services
Move keyword arguments to maintain API compatibility
Change order of arguments to maintain API compatilibity in the ServiceImpl constructor
Fix indentation
Re-add whitespace