Add logger to pip2

[michaeta]

As pip2 grows, it will become paramount that a logger will be required for continued development. Unlike pip, we will probably not want to implement our own logger on top of the standard python one. Currently all needed functionality is provided by the default python logger.

pip2 logging structure:

• log all uncaught exceptions with tracebacks
• log packaging/distutils2 logs to pip2's log with clear distinctions between the two
• pip2 log file gets reset after each time it is ran
• all pip2 standard output gets logged
• all logs will include time stamp, logger name, log level, and message

optional future log ideas:

• allow user to set the logging level of pip2 in a config file
• allow user to specify a path for the log file (for their own records) which will not get reset

[michaeta]

There are two possible methods I was thinking of when making sure that there were distinctions between the pip2 and packaging/distutils2 logger. One method was to include the logger's name in each log and the other was to have an extra log statement when loggers change.

First method:

pip2: message
pip2: mesage
packaging: message
packaging: message
pip2: message

second method:

message
message
===== packaging =====
message
message
===== pip2 =====
message

Any advice or recommendations on these approaches?