[Inkscape-devel] front page edit

In the spirit of "patch first, ask later", I have edited the intro paragraphs at inkscape.org: added new features, removed mention of GTKmm (it's on hold, and in any case this is a too narrow technical aspect to deserve a front page mention), added more emphasis on usability and general availability (it's not for "open source community", it's for everyone!) and did a general copyedit. Feel free to change :)