Adding function call with literals
Added constraints for nonrecursive calls and type equivalent calls
Updated documentation (issue #1)
some minor refactorings/docs from AlloyInspector
thowing exception for unimplemented method related to function calls
Updated documentation
Added code to get returned function call from model
Added necessary information about returning function call
Implemented function calls
Fixed function return constraint
Update README.md
Update SynthesisUnit.java

- Added hook for adding function prototype
- Reorganized methods
Added function prototypes (Issue #6)
Removed development instructions