Added initial support for ~ place holders.

- Modified Natlab parser (languages/Natlab/src/parser/natlab.parser) so
  that ~ (token NOT) is accepted in the input parameters of a function
  and also inside a matrix row.
- Modified Matlab parser (languages/Matlab/src/Matlab.g) so that
  ~ (token t_NOT) is accepted in the input parameters of a function and
  inside a matrix row.
- NOT/t_NOT is replaced in the AST with a Name("~") node.
- Change successfully parses many examples from MATLAB file exchange;
  we have not checked that semantic behavior is correct yet.