broker integration: add API documentation (broxygen/doxygen)

Also changed asynchronous data store query code a bit; trying to make
memory management and handling of corner cases a bit clearer (former
maybe could still be better, but I need to lookup queries by memory
address to associate response cookies to them, and so wrapping pointers
kind of just gets in the way).

src/Trigger.h

@@ -55,6 +55,8 @@ public:
 	// may not immediately delete it as other references may still exist.
 	void Disable();
 
+	bool Disabled() const { return disabled; }
+
 	virtual void Describe(ODesc* d) const { d->Add("<trigger>"); }
 
 	// Overidden from Notifier.  We queue the trigger and evaluate it