Add missing 4.0.0 Changelog
Update README.html

to point to "Smack 4 Readme and Upgrade Guide" DOC-2703
Fix documentation to use correct XMPPConnection names

Some parts of the documentation still refer to

Connection connection = new XMPPConnection(…)

when it should be

XMPPConnection connection = new XMPPTCPConnection(…)

SMACK-574