Don't allow unloading _core

Prevents getting stuck with no way of administrating the bot

README.md

@@ -37,9 +37,7 @@ async def handler(event):
 
 The core features offered by the custom `TelegramClient` live under the
 [`uniborg/`](https://github.com/uniborg/uniborg/tree/master/uniborg)
-directory, with some utilities, enhancements and the core plugin, which
-can be unloaded in itself (something fun to do, but you will probably
-want to restart your borg after).
+directory, with some utilities, enhancements and the core plugin.
 
 ## learning
 

uniborg/_core.py

@@ -36,7 +36,9 @@ async def remove(event):
     await event.delete()
     shortname = event.pattern_match["shortname"]
 
-    if shortname in borg._plugins:
+    if shortname == "_core":
+        msg = await event.respond(f"Not removing {shortname}")
+    elif shortname in borg._plugins:
         borg.remove_plugin(shortname)
         msg = await event.respond(f"Removed plugin {shortname}")
     else: