In the package Pandoc a function called `Get_Type()` is defined,
which takes a JSON block and returns the pandoc assigned type.
The main code of the `Traverse_Block` function is changed to
use an enumeration of Pandoc types instead of comparing string.
I've found, that wikibook has just part of Section 5, so I converted
missing text from html and put it on the wikibook. I put here the
conversion script just in case. Probably we can reuse it if we
will work on restoring links present in HTML, but lost on wikibook.
