Changelog

Next version: 0.9.1

LinearLayout:
- Better geometry computation with constrained size
- Fixed cache invalidation
- Fix possible panic when removing children
ScrollView:
- Fix possible panic with full-height scrollbar
- Fix possible panic with empty content
- Fix cache
Fix menubar focus after action

Add generic ScrollView wrapper. Removes internal scrolling behaviour from TextView.
Callbacks sent through Cursive::cb_sink() are now processed instantly, without the need for set_fps.
Make backend a dynamic choice
- User must select a backend in Cursive::new
- 3rd party libraries do not need to play with backend features anymore
Move from chan and chan-signals to crossbeam-channel and signal-hook
Batch-process events for higher performance
Add StackView::find_layer_from_id
Add SelectView::insert_item
Add TextArea::{enable, disable}
Reworked AnyView
SelectView: Fix mouse events
Return callbacks from manual control methods
- SelectView::{set_selection, select_up, select_down, remove_item}
- EditView::{set_content, insert, remove}
Add rect::Rect

Renamed Vec4 to Margins
Callbacks cannot be created from functions that return a value
- The returned value used to be completely ignored
AnyView does not extend View anymore (instead, View extends AnyView)
- If you were using AnyView before, you probably need to replace it with View
Scrolling is now added to a view with .scrollable()
cb_sink is now a crossbeam_channel::Sender instead of chan::Sender
SelectView::selection now returns an Option<Rc<T>> instead of just Rc<T>. It will return None if the SelectView is empty.

Style (breaking change):
- Added support for bold/italic/underlined text
- Added StyledString for markup text
- Refactored line-break module
Colors (breaking change):
- Added ColorStyle and PaletteColor for more flexible colored text
Buttons:
- Added Dialog::buttons to iterate on buttons
- Added Button::set_label and Button::label
TextView:
- Added TextContent, a way to separate model and view for TextView
- Added manual scrolling methods
Allow multiple global callbacks per event
Allow buttons and delimiters in top-level menubar
StackView:
- Added StackView::move_layer to re-order layers
- StackView::pop_layer now returns the pop'ed view
- Added StackView::reposition_layer to move a layer around
Dialog: added Dialog::focus(&self)
SelectView: added SelectView::selected
Cursive::cb_sink now accepts FnOnce (previously Fn only)