Replace StringBuffer with StringBuilder

In 2004 Java 5.0 was released with a note in StringBuffer's Javadoc

> As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.

Perhaps its is time to use StringBuilder as it is a drop in replacement. esp as this class is used heavily.