write and read InfluxDB LineProtocol

 The InfluxDB time series database (since version 0.9) uses a LineProtocol
 to write time series data into the database. InfluxDB::LineProtocol makes
 it possible to generate such a line from a data-structure, handling all
 the annoying escaping and sorting. It can also be used to parse a line
 (perhaps produced by other code) so that it can be further modified.