Add daemonic option

Normally, the Connection thread prevents program exit unless
close() is explicitly closed, unless `deaemonic=True` is passed.

It defaults to `False` which means aiosqlite's behaviour remains unaffected.

This PR would also address issues which have been opened for some time now:
omnilib#74
omnilib#299

aiosqlite/core.py

@@ -58,8 +58,9 @@ def __init__(
         connector: Callable[[], sqlite3.Connection],
         iter_chunk_size: int,
         loop: Optional[asyncio.AbstractEventLoop] = None,
+        daemonic: bool = False,
     ) -> None:
-        super().__init__()
+        super().__init__(daemon=daemonic)
         self._running = True
         self._connection: Optional[sqlite3.Connection] = None
         self._connector = connector
@@ -371,6 +372,7 @@ def connect(
     *,
     iter_chunk_size=64,
     loop: Optional[asyncio.AbstractEventLoop] = None,
+    daemonic: bool = False,
     **kwargs: Any,
 ) -> Connection:
     """Create and return a connection proxy to the sqlite database."""
@@ -391,4 +393,4 @@ def connector() -> sqlite3.Connection:
 
         return sqlite3.connect(loc, **kwargs)
 
-    return Connection(connector, iter_chunk_size)
+    return Connection(connector, iter_chunk_size, daemonic)