Fix More Javadoc Warnings

There are a couple of Javadoc warnings to the point where the project
will not build with the Java 8 Javadoc DocLint [1].

This change includes the following:
- replace &lt;p/&gt; (an empty paragraph) with &lt;p&gt; with starts a new
  paragraph
- replace &lt; and &gt; with &amp;lt; and &amp;gt; in a couple of places
- correct indentation of code in Javadoc in some places
- remove a stray &gt; in one place
- make all Javadoc lines start with *
- fix a @see reference

I did sign the Terracotta Contributor Argreement.

 [1] http://openjdk.java.net/jeps/172