Add pratlog backup script to text file

Usage: python -m chat.scripts.backup_pratlog -d '2013-08-24'

Backup the given date of chats into a txt file named:
  pratlog.[channel name].[date].txt
Log script:Add docstring, use .format() for string
Log script: Move Mongo initialization into method
Log Script: Add alternate config support
Log Script: Add log dir option, fix file handles

setdefault's second argument is always called, causing the file to be open
multiple times
Log Script: Better docstrings for script and args
Merge pull request #96 from stevetan/pratlog

Pratlog