support for logging to file instead of console

the line endings make comparisons more difficult but there are four parts:
1. TeX.py adds a call to Logging/fileLogging(). 
2. This method removes all the streamHandlers and adds a FileHandler and a filter. 
3. Config adds a switch (--log) to turn on logging to file instead of console
4. plastex script invokes the filelogging on the TeX instance if it the switch was given in the config.

"Assigning" to you for code review at your convenience!