Format updates in doc for topic routing and event flattening SMTs

In topic-routing.adoc and event-flattening.adoc:

• Replace conditionalized long/short headings with annotations.
• Add an introductory sentence after the heading in the config options section.
• Standardize on “option” and not “property” except in the anchor IDs.
• Change SMT references to plain text and not fixed width name of the actual SMT.

• Insert {zwsp} as needed to ensure option names in tables break only at the periods. 

These changes make this doc consistent with the more recently updated doc for other SMTs. These updates are needed in 1.3. They are not needed in the 1.2 branch.