VERITY TO-DO
Things that need to be done or should be done:
 - Consider changing the non-plain text XOR symbol to U+2295 (and accept '+' as
   XOR for input?)
 - Improve the quality of the PostScript output:
  - Make the dot in the XOR symbol actually be centered
  - Lower the tops of the vertical bars & lower their bottoms
  - Lower the horizontal bars a bit?
  - Center the tables?
  - Adjust the spacing between symbols?
 - Handle PostScript tables that approach the bottom of the page (and ones that
   are too wide for the page?)
 - Implement error recovery up to the next EOL (though symbols that are only
   referenced in erroneous rules will need to be purged somehow...)

Ideas for possible new features:
 - Add an option to output UTF-8 operator symbols in plain text mode
 - Make commas valid statement delimiters
 - Allow multi-block files to alternate between braces-enclosed statements and
   unenclosed statements (maybe)
 - Add a "<-" operator
 - Implement a way for users to define their own boolean functions/operators
  - All function names are single letters (or possibly one of a small set of
    punctuation marks), and if a binary function is used between two variables
    without parentheses around any arguments, it is interpreted as a binary
    operator (and this use should be honored in the output notation).
  - Possible example syntax: ``S(p, q) := p ^ -q''; ":=" and ':' should
    probably become alternate forms of each other.
  - It should be possible to define functions outside of statement blocks,
    thereby making them available for all subsequent blocks.
 - Implement non-standalone PostScript output
 - Implement embedded PostScript output
 - Implement *roff/tbl(1) output
 - Support variable names of arbitrary length
 - Sort variables in the tables in alphabetical order
