Organize and clean up Python implementation.

python/heck/exceptions.py

@@ -0,0 +1,20 @@
+"""
+Exceptions for HECKfile processing.
+"""
+
+class HeckException (BaseException):
+    """
+    Base exception for HECKfile processing.
+    """
+
+
+class HeckParseException(HeckException):
+    """
+    Raised for parse errors specifically.
+    """
+
+
+class HeckLexException(HeckException):
+    """
+    Raised for lex errors specifically.
+    """