Rename popover "anchor" to "side"

I don't think "anchor" makes sense unless I invert the words (so
anchor = "bottom" would mean the popup is above the parent).

Hopefully no-one was relying on this yet (though there was a warning
about breaking changes).

doc/popovers.md

@@ -41,13 +41,13 @@ gui.VBox{
             padding = 0.2,
             bgcolor = "#222e",
 
-            -- "anchor" specifies how the popover is positioned relative to the
+            -- "side" specifies how the popover is positioned relative to the
             -- parent, and can be "bottom" (default), "top", "left", or "right".
-            anchor = ctx.form.anchor,
+            side = ctx.form.side,
 
             -- align_h and align_v align the popover according to its parent
             -- element. You only need to specify align_h for
-            -- anchor = "top"/"bottom" or align_v for anchor = "left"/"right",
+            -- side = "top"/"bottom" or align_v for side = "left"/"right",
             -- this example specifies both so that it can demonstrate switching
             -- between different anchor types.
             align_h = "fill",
@@ -56,7 +56,7 @@ gui.VBox{
             -- Popover contents
             gui.Label{label = "Hi there!"},
             gui.Dropdown{
-                name = "anchor",
+                name = "side",
                 items = {
                     "bottom",
                     "top",

popover.lua

@@ -34,17 +34,17 @@ local function handle_popovers(box, node)
         local p_w, p_h = apply_padding(popover, 0, 0)
         local n_w, n_h = get_and_fill_in_sizes(node)
 
-        if popover.anchor == "top" then
+        if popover.side == "top" then
             offset_y = offset_y - p_h
-        elseif popover.anchor == "left" then
+        elseif popover.side == "left" then
             offset_x = offset_x - p_w
-        elseif popover.anchor == "right" then
+        elseif popover.side == "right" then
             offset_x = offset_x + n_w
         else
             offset_y = offset_y + n_h
         end
 
-        if popover.anchor == "left" or popover.anchor == "right" then
+        if popover.side == "left" or popover.side == "right" then
             align_types[popover.align_v or "auto"](popover, "y", "h", n_h - p_h)
         else
             align_types[popover.align_h or "auto"](popover, "x", "w", n_w - p_w)