Fix < and > Javadoc Warnings

There are a few more Javadoc warnings to the point where the project
will not build with the Java 8 Javadoc DocLint [1].

This change includes the following:

 * replace < and > with &lt; and &gt; in one place

I did sign the Terracotta Contributor Argreement.

 [1] http://openjdk.java.net/jeps/172