Dom handler fixes

[doj]

Fix #79

These changes fix the DOM handler:

• create a ROOT node as described in the description in the dom.lua file.
• place the DECL node as the first child node of ROOT if present.
• place the DTD node as the second child node of ROOT if present.
• place the root ELEMENT node as the third child node of ROOT.
• add a function dom:toXml(node) that will create a XML formatted string of a DOM ROOT node.
• fix some typos.
• remove some trailing whitespace.

[manoelcampos]

Since you based your changes on top of the previous PR, there are changes here which were already merged in the previous PR. Please perform a rebase to update your branch.

[manoelcampos]

Thanks for your contribution.