Add a .toEscapedXML() method in Verb.java

The .toXML() method doesn't escape the verb body by default (which it
should). However, for backwards compatibility, keep the behavior of the
old method the same and add a new method that does this for you.
Changel twiml response example to use .toEscapedXML()

User the safer method instead of .toXML()
Merge pull request #111 from juggernaut/xml-escaping

Add a .toEscapedXML() method in Verb.java