Completely change errors (make one class for each)

telethon/errors/rpc_errors_420.py

@@ -0,0 +1,16 @@
+from . import FloodError
+
+
+class FloodWaitError(FloodError):
+    def __init__(self, **kwargs):
+        self.seconds = kwargs['extra']
+        super(Exception, self).__init__(
+            self,
+            'A wait of {} seconds is required.'
+            .format(self.seconds)
+        )
+
+
+rpc_420_errors = {
+    'FLOOD_WAIT_(\d+)': FloodWaitError
+}