Add documentation for migrating from Hive
Add missing Cassandra decimal data type mappings
fix NPE in CassandraColumnHandle toString()
Parallelize test queries in presto-main

Make all unit tests in presto-main run in parallel by default, and
annotate non-threadsafe tests with singleThreaded=true
Fix bugs of upper case Cassandra schema, table, column names
Add backpressure to InMemoryExchange