Release Notes - Apache Tephra - 0.10.0-incubating

Improvements:
[TEPHRA-185] TransactionContext should support a custom transaction timeout
[TEPHRA-188] Provide a way to limit the transaction timeout
[TEPHRA-202] Bump twill dependency to 0.8.0

Bug fixes:
[TEPHRA-201] Fix an issue where in-progress transactions may become visible when transactions are checkpointed
[TEPHRA-194] Transaction client should not retry startShort() if an invalid timeout is given