Adding rudimentary socket receive support.
Moving message header into its own struct, so it can be used while parsing incoming messages.
Renaming NetworkMagicValue to just Network.
Merge branch 'master' of https://github.com/DoubleSha/BitcoinSwift

Conflicts:
	BitcoinSwift.xcodeproj/project.pbxproj
	BitcoinSwift/Message.swift