Make scriptTasak to use right syntax.
Re-orgnize source directory structure.
Seperate class ProcessInst from Process
Activity without incoming sequence flow must be instantiated when the process is intantiated.
Add bpmn.engine singleton.
Refine get next token algorithm
Introduce ActivityInst class.
Support Resource and ResourceParameter.
Use metaclass to register all models.
Re-org dirs, use bpmn.models to hold all BPMN Models
Refactor model classes with declarational programming.
Make test_usertask passed.
Support ExclusiveGateway, not completed.
Support Definitions element.
Remove useless symbol link.