Fix Language for v0.2

[CxRes]

Made Changes to language for 0.2

• Fixed use of Subscription in Abstract and Introduction.
• Added some intro text to Overview to contextualize diagrams.
• Modified intro text for the Protocol section. Add context for channel types.
• Cleaned up feature and broke into paragraphs.
• Fixed Data Models to be more precise.
• Small semantic and grammar changes.

[CxRes]

I have been moderately aggressive with the changes. If you have questions, I would be happy to walk you through why I felt a change was needed.

[csarven]

Merging this at this point as all mostly editorial changes are now in place.