A precedence parser, precedence table generator, and table interpreter.

The basis is a precedence relation function, in precedence.c, which, given a
grammar, will for any two tokens determine their precedence relation by
searching the grammar.

This function can be used directly by the parser, in parser.c, or can be used
by the precedence table generator, in table.c, to generate a table (in C),
which is then compiled with parser.c to obtain a much faster parser.