Coding style.

Using asyncio coroutines for workers instead of threads.

tools.py

@@ -4,6 +4,7 @@
 # Licensed under the Artistic License 2.0.
 
 import ast
+import asyncio
 import contextlib
 import dis
 import enum
@@ -654,7 +655,8 @@ class Result:
         self.status = status
         self.entry.appearance_cache = None
 
-    def run(self, log, appearance_changed_event, worker, runner):
+    @asyncio.coroutine
+    def run(self, log, appearance_changed_event, runner):
         self.is_placeholder = False
         tool_name = tool_name_colored(self.tool, self.path)
         path = path_colored(self.path)
@@ -665,7 +667,7 @@ class Result:
             runner.pause()
         appearance_changed_event.set()
         start_time = time.time()
-        new_status = worker.run_tool(self.path, self.tool)
+        new_status = yield from runner.run_tool(self.path, self.tool)
         Result.result.fget.evict(self)
         end_time = time.time()
         self.set_status(new_status)