Parser AST and Activity framework updates

[derek-pryor]

Parser updates:

• Created Abstract Syntax Tree (AST) that the parser creates and then is transformed into the JSON output
• Allows for targeted error messages that include the line and location of the error
• Parser updates cleaned up the parser code

Activity updates:

• Created two Mixins to contain the Activity and Task logic, so they can be implemented in multiple ways
• Re-implemented the existing Activity and Task Processes using the new mixins
• Improved Activity framework logging, should get a full stack trace in the log when an exception is detected

Considering these updates Heaviside v1.0

[derek-pryor]

Updated and expanded the documentation about the transform block. Agree that the wording of the statement was not understandable. Also discovered that ChoiceStates should not contain a ResultsPath, so modified the parser to correctly error in that case.