Actions proposal (#193)

* Add original proposal

* Reformat and revise some of the information

* Fix missing close preformat

* ROS 2 action server always generates goal id

* Rough description of services and topics

* ROS 1 cancels goals with stamps less than or equal to given time

* Add API section for action server

* Actions implemented in rcl

* More italics

* QoS warning for goal submission service

* Add API section for action client

* call -> calls

* Server discards result after giving it to the client

* Actions namespaced separately from msg and srv definitions

* Shrink possible statuses

* Replace high-level API section with details about goal states

Includes a state machine diagram for reference.

* Begin section about bridging ROS 1 and ROS 2

* Add Action Server C++ examples

* Move SimpleActionServer example to separate section

* Add include and type alias to action server example

* Add Action Client C++ examples

* Bridge R1 client and R2 server expanded

* Move API examples to examples repo

Added references to specific packages.

* Rough start to bridging ROS 1 server and ROS 2 client

* Update goal state machine

Rename ACTIVE -> EXECUTING and intermediate states to 'active' states.
Also added a transition from EXECUTING to CANCELED.

* Move bridge to bottom

* Link to python actions api

* minor grammar

* Update background

* Move Goal identifier section and add more rationale

* Minor wording in goal subscription service section

* Simplify explanation of why actions aren't in rmw

* Reword goalid sentences

* Stub alternatives section

* Start section of ROS 1 vs ROS 2 and move stuff to it

* Delete content in bridge section

* Remove realtime section stub

* Services promoted to 1 section type higher

* Move rmw note to alternatives section

* More content in differences section

* move differences higher up

* specification -> Interface Definition

* Add goal lifecycle examples

* Note about visibility of topics and services

* Shorten abstract

* Rename 'goal lifecycle' examples to 'interaction' examples

* Shorten introduction section

* Shorten sentence

* Minor rewording at start

* Reword/reformat section about entities involved in an action

* Make fragments in Action Inteface Definition complete sentences

* Introdice state machine before diagram

* move introspection tools section higher

* Slight formating chnages to introspection tools section

* Status topic is a list

* grammar requires ;

* 1 sentece becomes 2

* Add actions interaction overview diagram

* Update goal state machine

* Fix typos and grammer, consistency in lingo, and let action clients generate goal IDs as UUIDs

* Add a couple sentences regarding QoS for action feedback and status topics

* Add section about using multiple topics for feedback/status in 'Alternatives'

* Fix logic in cancel policy

* Minor clarifications

* Add topic and service name generation

* Address feedback from review

* Update authors
* Update description of Cancel Service response
* Minor wording change related to feedback and status topics

* Add sub-section to alternavtives on action server goal ID generation

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Update interaction example diagram

Add arrow depicting user execution method being notified of cancel event

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Fix author line

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Add third action interfaction example

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Fix typos, broken link, and rename goal events

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

Author: sloretz