Use lua callbacks for "interesting" textual effects
Description
The package allows manipulations of any LuaTeX document (it is
known to work with Plain LuaTeX and LuaLaTeX). Most of the
package's functions are merely for fun or educational use, but
some functions (for example, colorstretch for visualising the
badness and font expansion of each line, and letterspaceadjust
doing what its name says) could be useful in a "normal" LuaTeX
document.
