Merge lp://staging/~andrea.corbellini/a4/parser into lp://staging/a4

Parse the SVG file to look for presentation information.

This code looks for a <metadata> tag with the id "a4-presentation-information" into the SVG file. This tag will contain all the information about the presentation (e.g. the path and the sequence of animations).

Here's how you can test this change:

1. with your favorite editor, create an SVG document;
2. open it with a text editor and put into the root element (<svg>) the following code:

  <metadata id="a4-presentation-information">{"key": "value"}</metadata>

3. save and open the file with A4.

Now, if you introspect the a4lib.presentation.Presentation object you should see that its `information` attribute contains exactly this value:

  {u'key': u'value'}

See also my mail to the mailing list.