Remove "again" from "side effects per subscription" heading
Better phrasing for what signals represent
Add a heading to explain stream naming
"Handling asynchronous data sources" use case
"Chaining dependencies" use case
"Parallelizing work" use case
Minor code formatting cleanup
"Collection transformations" use case
Clarify "event delivery" contract heading
Merge branch 'design-guidelines' of https://github.com/ReactiveCocoa/ReactiveCocoa into design-guidelines

Conflicts:
	Documentation/DesignGuidelines.md
Updated 'Side effects occur for each subscription' following PR suggestions