* Set logging levels in Makefile using -DRAY_COMMON_LOG_LEVEL=level
* Lower level of some LOG_ERROR messages, log the name of the table operation on failure
* Address rest of Robert's comments
* Fix spurious log message
* Merge task table and task log
* Fix test in db tests
* Address Robert's comments and some better error checking
* Add a LOG_FATAL that exits the program
* Put infrastructure in place to compute task IDs and object IDs.
* Fix version number for common library.
* Compute task IDs and object IDs deterministically.
* Address Stephanie's comments.
* Update task documentation.
* Fix formatting.
* Add more tests and checks.
* Fix formatting.
* Enable DCHECKs and change CHECKs to DCHECKs.