Implement throwing exceptions.

include/pyliblexmodule.h

@@ -8,6 +8,9 @@ static PyObject* pyliblex_add_definition(PyObject* self, PyObject* args);
 static PyObject* pyliblex_lex(PyObject* self, PyObject* args);
 static PyObject* pyliblex_test(PyObject* self, PyObject* args);
 
+static PyObject* invalid_regex_exception;
+static PyObject* failed_lex_exception;
+
 static const char module_docstring[] = "A wrapper around a homemade lexing library, liblex.";
 static PyMethodDef module_methods[] = {
   {"init", pyliblex_init, METH_VARARGS, "Initialize a liblex library object." },