lib: add convenience debugging macros

lib: add convenience debugging macros

* Add DEBUG*() macros

This set of macros allows you to write printf-like debugging lines that
automatically check whether a debug is on before printing. This should
eliminate the need for explicit checks in simple cases. For example:

	if (SUCH_AND_SUCH_DEBUG_IS_ON) {
		zlog_warn(...);
	}

Becomes:

	DEBUG(warn, such_and_such, ...);

Or, equivalently,

	DEBUGE(such_and_such, ...);

The levels passed to DEBUG are expanded into the names of zlog_*
functions, so the same zlog levels are available. There's also a set of
macros that have the level built into them; DEBUGE for errors, DEBUGW
for warnings, etc. Good for brevity.

* Add singular setting macros

Change the 'SET' macros to accept a boolean indicating whether the
provided bits should be set or unset, and map on/off macros to them.
Helps condense code where you already have a boolean condition that
tells you what you want to do as you can avoid writing the branch.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>