Changing database schema: rename cron_error to cron_job because there can be logged every job now, not just errors
Adding logOnlyErrorJobsToDatabase trigger and method to enable database logging for all jobs - not only errors
Fixing the expression validator to enable six star expressions (* * * * * *<- last one is optional for year)
Expending the return value database logging - now booleans are displayed as strings
Fixing variable names - now they have much better names
Fixing some comments
Adding test case for logging all jobs to database
Adding test case for test database job return values
Preparing the readme for Cron v 0.9.