added getBufferedLogger function.

This function should be useful when you need to log during async
parallel operations, without having a mess in logs.
For example when you walk asynchronously a directory and you want logs
to be grouped by file.

It returns the same getLogger() object but messages are stored
internally and sent to appenders only when you call the flush() method
on it.
getBufferedLogger tested.
gitignore
Merge pull request #231 from eurekaa/buffered-logger

added getBufferedLogger function.