Remove '()' decoration from $caller internal variable. Decorations are
matter of presentations; at this level the brackets are only confusing.

To decide whether a caller is main script or direct descendant thereof,
called main(), use negative index of the stack array FUNCNAME (0 in first
case, 1 in the second).  To signal that to the `_pretty_*` plug-ins,
use a dedicated boolean.

This also accounts for cases when a main() function is declared somewhere
else than in the main binary.  Older code would simply assume (based
on the name being "main") that it's called from main binary and rewrite
$caller, possibly causing confusion.  Now, only the originally intended
special cases behave specially.

 *  Do not split text per line,
 *  use `<pre/>` for main text,
 *  use `<span />` for debug headers,
 *  and use more suitable class names.

A more conventional hierarchy

Ans its internal sub-modules to _pretty_*