Add sections about who this manual is for and how to read it
Restructure the content to facilitate the most common use case

namely writing of braille translation tables
Drop all node pointers

Take advantage of the implicit node pointer creation  feature in
makeinfo. This greatly simplifies the editing of the texi file.
Add Joseph's introduction to table writing
Add a NEWS entry for the documentation updates
Merge pull request #27 from liblouis/feature/doc_update

Documentation updates