[Feature Request] Save log to file

I appreciate the feature of grabbing the raw HTTP log for a transaction. But this only works if an exception is not thrown. I escpecially see good use for analysing the raw log when an exception has been thrown.

Therefore I am proposing that we set a file instead. Where your library can immediately dump the log to file once available.

`->setErrorLog('/path/to/desired/file.log')`
