v0.6.66

• [web] Added ability to edit attribute data of multiple selected features ("select features" tool).
• [web] Added interactive tool for adding points to point-type layer by clicking on the map.
• [web] Added "Add empty layer" button to the layers menu.
• [web] Added center handle for dragging the interactive box tool.
• Added -o fit-extent= option, to use a layer extent (typically a layer containing a single rectangle) for setting the extent of SVG output.