Added Log class

- Log class handles levels, messages, context, attributes
- Log levels are handled by the Log class
- Logger now creates Log objects to pass to handlers
- Modified handlers to use the Log class
renamed Logger class to Etcher
index properties use real class names

- changed etcher.log to etcher.Log, etc
- added test for index
Log messages can be set to an error

- The log message will be the error message
- The context 'error' key will be set to the error
Added createLog method
Context and attributes are now merged when using the object set methods
bubbling is now off by default for ChainLogHandler
Completed readme
Added docblocks
bumped version to 0.1.0