Well, this was an educational review!  You're now outputting column headers as the first row.  I see the 'every ::N' as a common solution for skipping N lines.  Is it necessary for 1 line?  The 'using' documentation says this:
```
If each column of data in the input file contains a label in the first row rather than a data value, this label can be used to identify the column on input and/or in the plot legend. 
```
The gnuplot script in plot.py for LevelDB charts spits out a head in the gnuplot data it generates and gnuplot doesn't complain and does the right thing.  Is the every::1 necessary?  If so, why doesn't gnuplot consider it a column header line?  (I mostly have to refresh my gnuplot knowledge details every time I look too closely.)

Otherwise I think your formatting changes are cleaner and get rid of a lot of string concats.  It isn't something I would have thought of myself, so thanks!