feat(Handlers): allow for configuration of log outputs

[beneboy]

Logga has so far been built just for capturing errors, not outputting them anywhere. Since existing logging solutions aren't configurable with files in a nice way, we could add this functionality to logga for configurable output.

{
    "level": "debug",
    "format": "${time} ${levelname} ${message}"
    "handlers": [
        {
            "type": "file",
            "path": "/path/to/file",
            "level": "warning"
        },
        {
            "type": "file",
            "path": "/errors/only",
            "level": "error"
        }
        {
            "type": "console",
            "level": "debug",
            "format": "${levelEmoji} ${levelName} ${time} ${message} ${trace}"
        },
        {
            "type": "syslog"
            "level": "error"
        }
    ],
    "loggas": {
        "stencila.encoda": {
            "handlers": []
        },
        "stencila.schema": {
            "level": "error",
            "handlers": [
                {
                "type": "console",
                "level": "debug"
                }
            ]
        }
    }
}

The message level must exceed both the handler level, global level and (if in a module) the module level to be logged somewhere.

If a logging module name is not found in the loggas dictionary it will fall back to the defaults.

Some examples:

log = getLogger('stencila.thema')
log.debug('some message')

Would log only to the console with a 🚨 emoji.

log.error('Some error')

Would log to /errors/only, /path/to/file, console and syslog. The syslog and file formats would be the global format.

encLogger = getLogger('stencila.encoda')
log.critical('some message')

Would not log anywhere as stencila.encoda has no handlers.

encLogger = getLogger('stencila.schema')
log.debug('some debug message')

Would not log anywhere because the stencila.schema log level is error so handlers can not override it.

There could be a standard list of default locations to look for a configuration file in, or passed in from the command line. (logga.json in the project dir, ~/.logga.json, /etc/logga.json etc)