 points, insert symbol codes
from the above list as a column along with the x-y data, and substitute
the command `<font color="#82140F"><code>read columns x y z</code></font>', and then draw them with
`<font color="#82140F"><code>draw symbol</code></font>'.  Gri will interpret the rounded-integer
values of the `<font color="#82140F"><code>z</code></font>' columns as symbol codes.  Note that even if
you've read in a z column which you intend to represent symbols, it will
be overridden if you designate a spec