rewrote the config system

there were many issues with the previous config system. A big one was
namespacing settings for different instances of the same executable.
Another was wanting to provide fallback to the conf file if command
line args weren't defined. A third was a desire for more reasonable
settings syntax: there were lots of getter funcitons with no real value.

now there is one way to both parse args, and to access the config file:
the squidwork.config.Config class. Please see the extensive docs in
conf2.yml and help(squidwork.config.Config)
document new config module