Added new exception.

gprMax/exceptions.py

@@ -16,6 +16,10 @@
 # You should have received a copy of the GNU General Public License
 # along with gprMax.  If not, see <http://www.gnu.org/licenses/>.
 
+class GeneralError(ValueError):
+    """Handles general errors. Subclasses the ValueError class."""
+    pass
+
 class CmdInputError(ValueError):
     """Handles errors in user specified commands. Subclasses the ValueError class."""
     pass