Use of libxml errors

If there has been any error in the wordpress xml export process, it
could be not well formed. This will show the error messages.
- Change namespaces from xml tags so the simplexml library does not die in panic
- tabs to spaces
Saving wordpress multiple categories and tags per post inside an extended post field
- Save categories and tags inside extended fields
- Common category for all the posts
- Save importer name (wp2anchor)

All this configurable inside the script turning true/false the $useMultipleCategories flag
Shorter field names to be viewed better inside the admin panel
Merge pull request #9 from neverbot/multiple_categories

Multiple categories