Added config to disable html escaping

[DracoBlue]

This patch makes it possible to use:

var ret = parser.process({
  "escapeHtml": true,
  "text": "I have some <iframe src='http://google.de'></iframe> for [b]you[/b]"
})
// ret.html: "I have some &lt;iframe src='http://google.de'&gt;&lt;/iframe&gt; for <b>you</b>"

or

var ret = parser.process({
  "escapeHtml": false,
  "text": "I have some <iframe src='http://google.de'></iframe> for [b]you[/b]"
})
// ret.html: "I have some <iframe src='http://google.de'></iframe> for <b>you</b>"

where escapeHtml is by default false to stay backwards compatible.