v0.6.6

* Disabled two concurrency unit tests since I believe they are flawed\r
  and do not yield reproducible results.\r
* Added Derby database dialect. Derby 10.7.1.1 and 10.8.1.2 pass 100%\r
  of tests.\r
* Implemented HSQL MERGE syntax. HSQL 2.2.4 fails 1 test which is a\r
  known bug in HSQL.\r
* Updated to H2 1.3.159\r