Adding 'deep' option in order to compare while ignoring whitespace in text nodes

As the title says, currently an XML like:
```code
<tag>
    Text content
</tag>
```
won't be equal to 
```code
<tag>Text content</tag>
```
So I just added the option to use the 'deep' flag in order to ignore whitespace at the beginning and end of the text nodes. It is done just setting to true the trim option in the xml2js parser.

Now, you can use expect(formattedXml).xml.to.deep.equal(unformattedXml) in order to ignore the whitespace or keep using expect(formattedXml).xml.to.not.equal(unformattedXml) in order to taking it into account.