move shared functionality to utility function added to Lepton library

lib/lepton/include/LMP_Lepton.h

@@ -32,6 +32,8 @@
  * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
  * -------------------------------------------------------------------------- */
 
+#include <string>
+
 #include "lepton/CompiledExpression.h"
 #include "lepton/CustomFunction.h"
 #include "lepton/ExpressionProgram.h"
@@ -40,4 +42,10 @@
 #include "lepton/ParsedExpression.h"
 #include "lepton/Parser.h"
 
+// utility functions
+namespace LMP_Lepton
+{
+  /// remove whitespace and quotes from expression string
+  std::string condense(const std::string &);
+}
 #endif /*LMP_LEPTON_H_*/