Projects, in no particular order:

- revise border command to use keywords
- clean up includes at the top of all files (string etc)
- put minor tics into demo file
- allow load '-' or  gnuplot -  to mean interactive

- define either quit or exit to mean finish-this-file, not finish session
  - at present, they are ignored in script files

longer term

- break it into four layers:
  : low lever graphics  (some of term.c)
  : plotting code, reading the setshow.h global variables
  : parsing code - read a string, and parse and execute it
  : front end, interact with terminal / gui
  basically, gplotlib is layer 2, and the traditional gnuplot is
  layer 4, which is little more than a small client of layer 3.
  Terminal option lines are table driven,
  so that even though the options are defined by layer 1, the
  actual parsing is implemented in level 3

- group related 'set' variables into structures, particularly xaxis
  stuff,etc. This will allow a move to table-driven parsing.
