Provide ability to temporarily configure the logger

[jonrkarr]

The current logging methods (set_formatter, set_level, file_logger) provide the ability to set logging globally. This creates the possiblity to two clients could configure the logger differently, causing problems for the other.

Two possible resolutions:

• Provide a way to set the formatter in a local context. Then each client can create its own separate, isolated configuration.
• Provide methods for getting the current logger configuration. Clients could then use to restore the global logger settings and they are finished.