[icon-artist] Add initial support for multiple icons in one source.
    Bump version to 0.1.95 as this is API/ABI change:
    * IconArtist::Icon.export now returns array.
      - typical expamle:
        [{"name" => "go-next", "context" => "actions",
          "sizes" => ["16x16","scalable"]},
         {"name" => "go-previous", "context" => "actions",
          "sizes" => ["16x16","scalable"]}]
    * IconArtist::Icon.symlinks are hashed by icon name.
      - typical example:
        {"go-next" => {:defalut => ["gtk-next"], :optional => []}}
    
    * IconArtist::THEME_SIZES expanded to include "64x64" and "128x128"