Add FunctionObject.ds
Copy FunctionObject.ds to bin folder
Update parameter type to var[]..[]
Remove redundant parameters
Add test cases for Apply() and Compose()
Add prefix "_" to FunctionObject class
Code emitter for imperative code

1. Extend CodegenDS to support emitting imperative ASTs
2. Testcases for CodegenDS imperative
Merge branch 'StableBranchWithTestcases' of https://github.com/lukechurch/designscript into JunStableBranch1
Merge pull request #165 from ke-yu/functionObject

Add FunctionObject.ds
Merge pull request #167 from junmendoza/JunStableBranch1

Imperative code emitter