* pep-550: Rename LocalContext -> LogicalContext
* pep-550: Rename ContextItem -> ContextKey
* pep-550: Update ContextKey caching
* pep-550: Reorder Generators and Coroutines sections; drop await/ceval
* pep-550: Some rewording in the HAMT Performance section
* pep-550: Add a couple of paragraphs to Approach 3
* pep-550: Add version 3 summary of changes
* pep-550: A few more edits
* pep-550: Update the Version History section
Yury Selivanov