gtk+ 3.20.10 release.

Bug fixes:

• 358970 gtk_scale_set_digits does not cause value to be rounded if draw-value is false...
• 767391 cross-fade() not cross-fading
• 770166 Can GtkButtons of arbitrary size be circular? The style class only accommodate...
• 770236 gtkbindings: Add an example for gtk_binding_entry_add_signal()
• 770242 gtkbindings: Clarify that widgets need has-focus for bindings to work
• 770332 Notebook arrow icon wrong color after creating new tab
• 770374 Gtk Treeview Editable overshoots column width when column width is small
• 770550 gtkplacessidebar: fix signal marshal
• 770614 GtkScale in HighContrast theme with value = 0: WARNING: allocates negative con...
• 770624 Fix typos.
• 770703 Fix crash when using page-down on GtkListBox
• 770849 GtkLabel with padding brokenness
• 774695 GtkProgressbar needs full and empty classes
• 774726 GtkTreeView dnd: gtk_drag_finish remove row when reorder sinse 3.20
• 775525 gtk_flow_box_get_child_at_index shouldn't crash with an invalid index
• 775864 getting-started: typo tie->the
• 776560 icon-browser: window opens at very narrow size, only showing 1 column of icons
• 779002 Race enumerating the monitors