C++ error handling enhancements

[stevencarlislewalker]

We have good localization of errors for expressions on the right hand side of before, during, and after formulas, but no localization for the left hand side or objective functions (e.g., #107).

While we are at it we probably want to allow for recursive evaluation of arguments passed to functions on the left hand side. So that we can do things like x[0:9] ~ y, which now requires that we explicitly pass an integer vector, say i = 0:9, and use x[i] ~ y. To do this we just need to create an expression evaluator for the assignment parse table, and pass this to the assigner so that it can be used when evaluating the arguments to function on the left hand side.

• localized error messages for objective function
• localized error messages for left hand side
• pass checks
• recursive evaluation of arguments to left hand side functions
• pass checks
• performance test against main