rename web_server to api (#29)

* add front end code

* change licence

* rename web_server to API

* change name to web_server

api/errors/__init__.py

@@ -0,0 +1,10 @@
+from .general_error import *
+
+
+class RagFlowError(Exception):
+    message = 'Unknown Rag Flow Error'
+
+    def __init__(self, message=None, *args, **kwargs):
+        message = str(message) if message is not None else self.message
+        message = message.format(*args, **kwargs)
+        super().__init__(message)