Move out arguments parser to a new module

Create a new module 'args' which do the arguments parsing job for the web
site. And add .gitignore file to ignore the .pyc file.
Move username to Website's instance variable

Instead of passing the 'username' parameter to Website's methods, move
it to a instance variable.
Add a logger method for Website

Complete the logger feature, now every visit will be recorded in the
visit.log file.
Merge branch 'feature/logger'
Add a login method for Website
Show a different welcome message if user is boss

This is a hotfix for showing different message to boss.
Add a logout method for Website
Merge branch 'feature/log-in-out'

Conflicts:
	args.py
Add the client privacy feature

Now clients can browse the web site in a private mode.
Add a show_stats method for Website

Now user can specify a '--view-stats' argument to get some statistics on
the web site.
Merge branch 'feature/client-privacy'
Merge branch 'feature/view-stats'

Conflicts:
	args.py