Logging Exceptions

[rofinn]

We can create a traceback when a Record is created, but sometimes we might want to pass in an exception to log.

Solution:

1. Support passing record attributes to log as keyword arguments.
2. Update the string formatting to support optional components (e.g., include traceback when it is already set.

[rofinn]

I think this will be related to #93, but I'm not sure if we want this for 1.0.