Adaptive worker thread count

cista/app.py

@@ -3,6 +3,7 @@ import datetime
 import mimetypes
 import threading
 from concurrent.futures import ThreadPoolExecutor
+from multiprocessing import cpu_count
 from pathlib import Path, PurePath, PurePosixPath
 from stat import S_IFDIR, S_IFREG
 from urllib.parse import unquote
@@ -33,8 +34,9 @@ app.exception(Exception)(handle_sanic_exception)
 @app.before_server_start
 async def main_start(app, loop):
     config.load_config()
+    N = max(2, min(8, cpu_count()))
     app.ctx.threadexec = ThreadPoolExecutor(
-        max_workers=3, thread_name_prefix="cista-ioworker"
+        max_workers=N, thread_name_prefix="cista-ioworker"
     )
     await watching.start(app, loop)