Stub out how we're actually generating code
Start validating the program.
Update to version of sexp library with Visitor pattern
Sketch out a basic Ast class hierarchy
Update sexp lib again
Add the AstVisitor as a constructor arg to Exec and Program
Differentiate between integers and commands
Have the AstVisitor dispatch to Program and ExecSeq
Finish up stub implementation of AstVisitor
Add ast.cpp to the compilation list
Update sexp lib again