Fix trivial spelling errors

- occured -> occurred
- reponse -> response
- seperated -> separated

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.

writeengine/splitter/we_filereadthread.cpp

@@ -204,7 +204,7 @@ void WEFileReadThread::setup(std::string FileName)
   catch (std::exception& ex)
   {
     // cout << ex.what() << endl;
-    // throw runtime_error("Exception occured in WEFileReadThread\n");
+    // throw runtime_error("Exception occurred in WEFileReadThread\n");
     throw runtime_error(ex.what());
   }