format --depgraph/--revdep output
add @header, @license section keywords

+ --extract-sections,-X: accept '^' and '!' for blacklisting sections
shlibcc: --enable-debug-code {yes,comment,no}

shlib modules/script may now decorate debug code with
"#@debug <shell code line>". Such code remains disabled if the shlib linker (or
the loader.sh helper) doesn't support it, because it's a comment.
With --enable-debug-code=y, it is transformed into real code by removing the
"#@debug" prefix.

Some @debug code shortcuts are provided:
* @debug_echo, @debug_print, @debug_stdout => @debug echo "<shell code line>"
* @debug_stderr => @debug echo "<shell code line>" 1>&2
* @debug_warn   => @debug echo "WARN: ..." 1>&2
* @debug_error  => @debug echo "ERROR: ..." 1>&2

Similar to --keep-safety-checks, passing "no"/"n" or "comment"/"c" to
--enable-debug-code=comment results in removing statements or
keeping them as comment lines.