This change lays the ground for automated unit tests. It adds
command-line options to select the input language format between URL
(hexa text) and plain text, change a few output settings, and redirect
graphical output to an image.
A text lexer has also been added so that unit tests and new programs can
be written in an English-like syntax instead of raw hexadecimal.
The program is currently able to lex most useful tokens, and parse
constructs associated with them on simple examples.
Unit tests are still missing to formally ensure everything's right.