[Inkscape-docs] splitting user manual

Howdy,

I'd like to start adding some new content soon. Do we have common agreement to split user manual into chapters and use <XInclude> to join them? If we do, I'll go ahead and do it.

Also, why do we use lang="en" attribute everywhere in inkscapeUTFen.xml?

Colin, I think we need a simple Makefile to create HTML version (at least HTML). Since my bash mojo is not so cool for last couple of years, maybe you could have a look? ;)

Alexandre