Rename subscribeOn to evaluateOn
Rename `on` block from `subscribed` to `started`
Remove subscriber terminology from ColdSignal docs
Remove subscriber terminology from other docs
Merge branch 'swift-development' into kill-subscription-terminology

Conflicts:
	ReactiveCocoa/Swift/Action.swift
Merge pull request #1622 from ReactiveCocoa/kill-subscription-terminology

Remove references to “subscribers” and “subscription” from Swift APIs