cleanup worker task logging

In order to avoid name conflicts with WorkerTaskContext

- renamed WorkerTask::log to WorkerTask::log_message

Note: Methods have different fuction signatures

Also renamed WorkerTask::warn to WorkerTask::log_warning for
consistency reasons.

Use the task_log!() and task_warn!() macros more often.

src/api2/reader/environment.rs

@@ -52,11 +52,11 @@ impl ReaderEnvironment {
     }
 
     pub fn log<S: AsRef<str>>(&self, msg: S) {
-        self.worker.log(msg);
+        self.worker.log_message(msg);
     }
 
     pub fn debug<S: AsRef<str>>(&self, msg: S) {
-        if self.debug { self.worker.log(msg); }
+        if self.debug { self.worker.log_message(msg); }
     }