code: function logfilter(options) {
    let level = options.level || 'info+'
  
    let calculatedLevels = []
  
    if (level_exists(level)) {
      calculatedLevels.push(level)
    } else if (_.endsWith(level, '+')) {
      // Level + notation
      calculatedLevels = log_level_plus(level.substring(0, level.length - 1))
    } else {
      // No level nor level+... it must be a custom alias
      let processedAliases = Object.assign({}, aliases, options.aliases)
      let aliasInfo = processedAliases[level]
      if (aliasInfo) {
        let handled = _.get(aliasInfo, 'handled', true)
        if (handled) {
          calculatedLevels = aliasInfo.handler(options)
        }
      }
    }
  
    return function filter(data) {
      if (calculatedLevels.indexOf(data.level) !== -1) {
        return data
        /*
        let cloned = _.clone(data)
        if (options['omit-metadata']) {
          cloned = _.omit(cloned, ['seneca', 'level', 'when'])
        }
  
        if (options.omit && _.isArray(options.omit)) {
          cloned = _.omit(cloned, options.omit)
        }
        return cloned
  */
      }
      return null
    }
  }
docs: TODO: needs massive refactor