A luigi task that writes to a local sparkey log file.
Subclasses should implement the requires and output methods. The output must be a luigi.LocalTarget.
The resulting sparkey log file will contain one entry for every line in the input, mapping from the first value to a tab-separated list of the rest of the line.
To generate a simple key-value index, yield “key”, “value” pairs from the input(s) to this task.