Add prepared stmnt cases to type tests
Handle tracing flags on encode/decode
Use logging for decoder warnings
Merge branch 'master' into tracing-support

Conflicts:
	cassandra/decoder.py
First draft of QueryTrace, TraceEvent classes
Fix bad trace body read, convert to UUID
Add __str__ for trace classes, friendlier types
Enable tracing through execute(_async)() kwarg only
Documentation for new tracing classes and attrs
Add method to retrieve query trace
Remove tracing from TODO list in README
Correct callback erroring when message can't be decoded
Add some missing tracing documentation