* Rename epaint feature "persistence" to "serialize"
* Add separate "serialize" feature to egui
* egui_demo_lib: separate serialize and persistence features
* Add App::persist_native_window and App::persist_egui_memory
Controls what gets persisted
* First pass (missing rendering the bar)
* Render horizontal bars, and change Window scroll API
* emath: add impl Index + IndexMut for Align2
* Scrolling: fix subtle sizing bugs
* Add horizontal scrolling to color test
* try to wrap content before showing scrollbars, + add auto-shrink option
* Add hscroll to the misc demo window
* Fix for putting wrapping labels in an infinitely wide layout
* Add a egui_asserts to protect against nans in the layout engine
* Add line about horizontal scrolling to changelog
* Add example to docs of ScrollArea
* code cleanup