[Firebird-docs] First 'new' documents online

[Mark R. <ma...@la...>]

I have migrated the first documents to asciidoc:

- Docbuilding Howto
   - HTML 
https://www.firebirdsql.org/file/documentation/html/en/firebirddocs/docbuildhowto/firebird-docbuilding-guide.html
   - PDF 
https://www.firebirdsql.org/file/documentation/pdf/en/firebirddocs/docbuildhowto/firebird-docbuilding-howto.pdf
- Docwriting Guide
   - HTML 
https://www.firebirdsql.org/file/documentation/html/en/firebirddocs/docwritehowto/firebird-docwriting-guide.html
   - PDF 
https://www.firebirdsql.org/file/documentation/pdf/en/firebirddocs/docwritehowto/firebird-docwriting-howto.pdf

I have also updated them to have information about the new situation.

I haven't updated the documentation index yet, because I first need to 
identify which redirects need to be added so old links continue to work.

Mark
-- 
Mark Rotteveel