Terminal definition file.

This module describes the options available to gnuplot's various terminals. For the moment, it only supports a few terminals, but the infrastructure is here to add others as they are needed.

Part of the trick is that the set terminal command takes myriad suboptions with various argument types, and order is sometimes significant. The other part of the trick is that there are over 50 terminal types, and each terminal has its own set of options.

The strategy here is to define a general mechanism for turning Python keyword parameters into fragments of gnuplot command strings. There are a number of classes derived from Arg that do this. Some take string args, some boolean, etc. Then the list of options that each terminal accepts is stored in the terminal_opts dictionary. Gnuplot.hardcopy(), in turn, uses this dictionary to interpret its keyword arguments and build the set terminal command.