Add verbatim option to preprocessor

Sometimes one would like to use a keyword detected by the preprocessor in a Matlab command, but the parsing detects this as invalid syntax. If possible, we should add something like a verbatim command to the preprocessor that adds the content without changing it to the m-file.

For example

verbatim(cellstr={'eps_a';'eps_b'};)

would write the content to the m-file without leading to an error as it currently does if eps_a is declared in var_exo