improvements to model printing with source

[Stephen Siegel]

The format for including source code in the model print out could be improved. This is an excerpt of what it looks like now:

begin model Impl
| begin input variables
| | N : int;
line 1 column 0 through line 1 column 25:
input int N{N>=0 && N<=2};
| | a : int[N];
line 2 column 0 through line 2 column 14:
input int[N] a;
| end input variables;
| begin output variables
| | s : real;
line 3 column 0 through line 3 column 13:
output real s;
| end output variables;
| begin process 0
| | main function : main;
Function signature: line 5 column 0 through line 5 column 10:
void main()
| | begin function main

It would look better if the source code could be incorporated into the tree-structure. Also, "line 5 column 0 through line 5 column 10" could be abbreviated like 5.0-5.10 to save space. Here is what it will look like:

begin model Impl
| begin input variables
| | N : int;
| | | foo.mmp 1.0-1.25 "input int N{N>=0 && N<=2};"
| | a : int[N];
| | | foo.mmp 2.0-2.14 "input int[N] a;"
| end input variables;
| begin output variables
| | s : real;
| | | foo.mmp 3.0-3.13 "output real s;"
| end output variables;
| begin process 0
| | main function : main;
| | begin function main

[ywei]

Changed as required.