Improved filters system

- `RoomEventData` is renamed to `EventContext` and moved to context.py
- `EventContext.filter` is removed
- Added context variables system which improves type hints and simplifies callbacks code
- `BodyCommandFilter` sets context variables from now on
- Added `super().__call__` invocation to filters implements in base.py
- Examples are updated to include required changes

examples/image_gen_bot.py

@@ -13,23 +13,15 @@ import logging
 import random
 from PIL import Image
 
-from mab import (
-    MatrixBot,
-    MatrixBotConfig,
-    RoomEventData,
-    MessageTypeFilter,
-    BodyCommandFilter,
-    SenderIsBotFilter,
-    MessageType
-)
+from mab import *
 
 from _environment import check_environment
 
-async def on_gen_command(data: RoomEventData) -> None:
+async def on_gen_command(data: EventContext) -> None:
     """This callback is called when `!gen R G B` command is received."""
     # convert R, G and B to floats
     try:
-        r, g, b = [float(v) for v in data.event.command_args] # type: ignore
+        r, g, b = [float(v) for v in data[CTX_CMD_ARGS]]
     except:
         await data.bot.send_text(data.room, "Invalid arguments")
         return
@@ -53,7 +45,7 @@ async def on_gen_command(data: RoomEventData) -> None:
     # send
     await data.bot.send_image_bytes(data.room, buf, "noise.png")
 
-async def on_wrong_message(data: RoomEventData) -> None:
+async def on_wrong_message(data: EventContext) -> None:
     """This callback is called when a wrong message is received."""
     await data.bot.send_text(
         data.room,