Update Specification with OTEP 66 changes

[carlosalberto]

This is an issue tracking the different PRs that add the changes in OTEP 66 to the Specification:

• Temporarily remove Binary format: Remove binary format propagator #426
• Add CorrelationContext API and remove DistributedContext: Adding Correlations API and removing DistributedContext #420
• Add the Context notion: Add the Context notion. #424
• Global and Composite Propagators: Initial composite/global Propagators update for OTEP 66. #440

[carlosalberto]

Closing this as the initial update has been completed!

We will follow up the needed improvements and clarifications as part of 0.4.0