Reverts 09a1f78 and instead ensures double quotes are escaped.

Double quotes should be used for identifiers - it's a quirk that Sqlite
accepts them for strings as well, but in the event we encounter them we
should escape them to try to keep valid Python.

Refs #2909

playhouse/reflection.py

@@ -92,7 +92,8 @@ def get_field_parameters(self):
         if self.primary_key and not issubclass(self.field_class, AutoField):
             params['primary_key'] = True
         if self.default is not None:
-            params['constraints'] = '[SQL(\'DEFAULT %s\')]' % self.default
+            params['constraints'] = '[SQL("DEFAULT %s")]' % \
+                    self.default.replace('"', '\\"')
 
         # Handle ForeignKeyField-specific attributes.
         if self.is_foreign_key():