Minor addition to WIKI Page and Book interfaces.

git-svn-id: https://svn.eiffel.com/eiffelstudio/trunk@95754 8089f293-4706-0410-a29e-feb5c42a2edf
- wiki_docs is now an Eiffel library itself.
- improved wiki book from simple plain text file storage (without book.index)

git-svn-id: https://svn.eiffel.com/eiffelstudio/trunk@95755 8089f293-4706-0410-a29e-feb5c42a2edf
Added initial documentation structure under data/documentation/current

git-svn-id: https://svn.eiffel.com/eiffelstudio/trunk@95756 8089f293-4706-0410-a29e-feb5c42a2edf