This commit changes how we check if a job's expression is due

On the run methond i added a boolean parameter checkRunTime
If true then the job expression due time is checked against the time on which the
run command was called
If false we use 'now'
Added 2 tests to check the behaviour of the new checkRuntime parameter in the run
method
Added a brief description of the new functionality to the README
Merge pull request #9 from problematik/checkruntime

Change how a jobs due time is calculated