v3.5.0

• Bindings are now not limited to main thread.
• ExecutionContext has been refactored into a struct.
• Few renames in order to be consistent with Swift standard library:
  • replay(_:) becomes replay(limit:).
  • flatMapLatest(transform:) becomes flatMapLatest(_:).
  • flatMapConcat(transform:) becomes flatMapConcat(_:).
  • flatMapMerge(transform:) becomes flatMapMerge(_:).
  • flatMapError(recover:) becomes flatMapError(_:).
  • filter(include:) becomes filter(_:).
• Significant README update.