Break out make_function() into its own file.

It is already too complex and will get worse in Python 3.6.

Note: make_function in fragments.py is still inside and
probably needs fixup.

uncompyle6/semantics/parser_error.py

@@ -0,0 +1,11 @@
+import uncompyle6.parser as python_parser
+class ParserError(python_parser.ParserError):
+    def __init__(self, error, tokens):
+        self.error = error # previous exception
+        self.tokens = tokens
+
+    def __str__(self):
+        lines = ['--- This code section failed: ---']
+        lines.extend([str(i) for i in self.tokens])
+        lines.extend( ['', str(self.error)] )
+        return '\n'.join(lines)