Make logLevel an instance variable instead of static

[armcknight]

We use this in an app with two different types of loggers, A and B which inherits from A. We are not able to set their log levels independently because the log level is statically defined on the class Log. If it were instance-level, then this connection would be broken and loggers would behave as expected when setting them to different levels.

[ZevEisenberg]

+1 or at least have a global for general-purpose static logging, but let you override it if you want to instantiate loggers other than the default/shared logger. Progressive disclosure.

[chrisballinger]

We just got bit by this again today.

[chrisballinger]

If we're keeping score, someone else got bit by this again today.

[ZevEisenberg]

Doooo eeeeet