Add String::isEmpty()

Author: alranel

api/String.h

@@ -89,6 +89,7 @@ class String
 	// invalid string (i.e., "if (s)" will be true afterwards)
 	bool reserve(unsigned int size);
 	inline unsigned int length(void) const {return len;}
+	inline bool isEmpty(void) const { return length() == 0; }
 
 	// creates a copy of the assigned value.  if the value is null or
 	// invalid, or if the memory allocation fails, the string will be