XML block datatype new features

*Title: XML block datatype new features.

*Description: XML block editing and publishing routines were completely
rewritten, which means that old bugs are no more there and new features
have been added.

*Features:

- Simplified XML input edit field shows much more well-formatted content.
  On the other hand it doesn't depends on user input formatting.
  
- Input errors are processed in more accurate way and user input is never
  erased or modified until it is correct.
  
- Introduced new tag "embed-inline'.
  See 'doc/eng-us/features/3.8/embed-inline.txt' for details.
  
- It is now possible to use inline tags inside headers. (including custom
  inline tags)
  
- Added possibility to define a way of processing space characters in eZXML
  input. This is controlled by the following settings:
  
    ezxml.ini:[InputSettings].TrimSpaces setting:
    True value means that spaces will be stripped off in the old way and false
    means that all spaces remain in place.
  
    ezxml.ini:[InputSettings].AllowMultipleSpaces setting:
    True means that space characters sequence will be replaced by one space
    character.
      
- Added possibility to allow empty paragraphs in the input. This is controlled
  by a setting:
    content.ini:[paragraph].AllowEmpty

- Automatic headers numeration allows you to use eztoc template operator to 
  automatically create tables of contents for your XML text fields. An anchor
  with unique ID is added to every header.
  See 'doc/eng-us/features/3.8/TOC_operator.txt' for details.