Add --app-dir option for running uvicorn from any location (#619)

Add '--app-dir' option to specify application directory when running uvicorn from any location
Closes #549

Author: yezyilomo

docs/deployment.md

@@ -87,6 +87,9 @@ Options:
                                   [default: TLSv1]
   --header TEXT                   Specify custom default HTTP response headers
                                   as a Name:Value pair
+  --app-dir TEXT                  Look for APP in the specified directory, by
+                                  adding this to the PYTHONPATH. Defaults to
+                                  the current working directory.
   --help                          Show this message and exit.
 ```
 

uvicorn/main.py

@@ -256,6 +256,13 @@ def print_version(ctx, param, value):
     is_eager=True,
     help="Display the uvicorn version and exit.",
 )
+@click.option(
+    "--app-dir",
+    "app_dir",
+    default=".",
+    show_default=True,
+    help="Look for APP in the specified directory, by adding this to the PYTHONPATH. Defaults to the current working directory.",
+)
 def main(
     app,
     host: str,
@@ -290,8 +297,9 @@ def main(
     ssl_ciphers: str,
     headers: typing.List[str],
     use_colors: bool,
+    app_dir: str,
 ):
-    sys.path.insert(0, ".")
+    sys.path.insert(0, app_dir)
 
     kwargs = {
         "app": app,