Protocol compatibility

• Fixes #24
• Made library compatible with swift 4.0 and swift 5.0
• Updated ping-pong synchronisation with respect to new client

Library Upgrade #15 #22

• Updated starscream and handyjson version to support swift 4.2
• Skipped volatile tests

Authentication while channel subscribe

• Auth Token can now be injected from constructor, getter and setter are now available for token
• Authentication while subscribing to channel. Extra argument can be given as a token to authenticate with server