Print result of evaluation in Ergo Syntax

[jeromesimeon]

When evaluating Ergo, it would be nice to have the option to print the result in Ergo syntax. Currently it uses JSON which does provide the information but can be a bit confusing since this is more like a serialization syntax.

This can be best illustrated with the REPL.

For:

$ ./bin/ergotop ./examples/helloworld/model.cto ./examples/helloworld/logic.ergo 
Welcome to ERGOTOP version 0.1.3
ergo$ import org.accordproject.helloworld.*
ergo$ set contract HelloWorld over TemplateModel{ name : "Tigger" }
ergo$ call helloworld(Request{ input : "Foorest" });
Response. {"type": ["org.accordproject.helloworld.Response"], "data": {"output": "Hello Tigger (Foorest)"}}

The response could be written as:

ergo$ call helloworld(Request{ input : "Foorest" });
Response. Response{ output : "Hello Tigger (Foorest)" }

or

ergo$ call helloworld(Request{ input : "Foorest" });
Response. ~org.accordproject.helloworld.Response{ output : "Hello Tigger (Foorest)" }

For:

ergo$ return 1;
Response. {"nat": 1.0}

The response could be written as:

ergo$ return 1;
Response. 1

For:

ergo$ define constant zenbear = "pooh"
ergo$ return Request{ input : zenbear };
Response. {"type": ["org.accordproject.helloworld.Request"], "data": {"input": "pooh"}}

The response could be written as:

ergo$ return Request{ input : zenbear };
Response. Request{ input: "pooh" }

For:

ergo$ return nil;
Response. null

The response could be written as:

ergo$ return nil;
Response. nil

(Or whichever syntax we use for an empty optional -- See discussion in #321)

[jeromesimeon]

Also for:

ergo$ return some(1.5 * 2.0);
Response. {"left": 3.0}

The response could be written as:

ergo$ return some(1.5 * 2.0);
Response. some(3.0)

[jeromesimeon]

Similar issues will arise when #2 and #3 are resolved

[kach]

#364