Fixed broken behavior when removing a page from a Notebook, now warns when trying to remove the last page of the notebook, added cond/endcond to EnableSharedFromThis and NonCopyable to clean up inheritance graph in doc (they didn't really provide useful information anyway since they are inherited by every class and shouldn't be used externally).
Fixed minor documentation error. #594
Added PackStart, PackEnd and ReorderChild to Box to make using it easier.
Added support for multiple pages in the texture atlas to support arbitrarily many images and image sizes (that themselves would fit on the GPU of course), added explicit sf::Context construction before querying GLee for supported extensions to fix special cases where no sf::Context is available yet thus making GLee report wrong extension information.
Fixed child widgets not notifying tentative parents of the child's invalidation if the invalidation took place before it was added to the parent and the next update cycle.
Fixed not taking into account padding when determining if the Renderer needs to create a new atlas page.