docs(btn, btnmatrix, calendar) upadte to v8

docs/widgets/btn.md

@@ -6,60 +6,28 @@
 
 ## Overview
 
-Buttons are simple rectangle-like objects. They are derived from [Containers](/widgets/cont) so [layout](/widgets/cont#layout) and [fit](/widgets/cont#fit) are also available. 
-Besides, it can be enabled to automatically go to checked state on click.
+Buttons has no new features compared to the [Base object](/widgets/obj). It usufule for semantic purposes and has slightly different default settings.
 
+Buttons differ from Base object in the following points by default:
+- Not scrollable
+- Added to the default group
+- Its default height and width is `LV_SIZE_CONTENT`
 
 ## Parts and Styles
-The buttons has only a main style called `LV_BTN_PART_MAIN` and it can use all the properties from the following groups:
-- background
-- border
-- outline
-- shadow
-- value
-- pattern
-- transitions
-
-It also uses the *padding* properties when *layout* or *fit* is enabled.
+- `LV_PART_MAIN` The background of the button. It uses the typical background style properties.
 
 ## Usage
 
-### States
-To make buttons usage simpler the button's state can be get with `lv_btn_get_state(btn)`. It returns one of the following values:
-- **LV_BTN_STATE_RELEASED**
-- **LV_BTN_STATE_PRESSED**
-- **LV_BTN_STATE_CHECKED_RELEASED**
-- **LV_BTN_STATE_CHECKED_PRESSED**
-- **LV_BTN_STATE_DISABLED**
-- **LV_BTN_STATE_CHECKED_DISABLED**
-
-With `lv_btn_set_state(btn, LV_BTN_STATE_...)` the buttons state can be changed manually.
-
-If a more precise description of the state is required (e.g. focused) the general `lv_obj_get_state(btn)` can be used.
-
-
-### Checkable
-You can configure the buttons as *toggle button* with `lv_btn_set_checkable(btn, true)`. In this case, on click, the button goes to `LV_STATE_CHECKED` state automatically, or back when clicked again.
-
-
-### Layout and Fit
-Similarly to [Containers](/widgets/cont), buttons also have layout and fit attributes.
-- `lv_btn_set_layout(btn, LV_LAYOUT_...) `set a layout. The default is `LV_LAYOUT_CENTER`.
-So, if you add a label, then it will be automatically aligned to the middle and can't be moved with `lv_obj_set_pos()`.
-You can disable the layout with `lv_btn_set_layout(btn, LV_LAYOUT_OFF)`.
-- `lv_btn_set_fit/fit2/fit4(btn, LV_FIT_..)` enables to set the button width and/or height automatically according to the children, parent, and fit type.
-
+There are no new features compared to [Base object](/widgets/obj).
 
 ## Events
-Besides the [Generic events](../overview/event.html#generic-events) the following [Special events](../overview/event.html#special-events) are sent by the buttons:
- - **LV_EVENT_VALUE_CHANGED** - sent when the button is toggled.
+- `LV_EVENT_VALUE_CHANGED` when the `LV_OBJ_FLAG_CHECKABLE` flag is enabled and the obejct clicked (on transition to/from the checked state)
+
 
 Learn more about [Events](/overview/event).
 
 ## Keys
-The following *Keys* are processed by the Buttons:
-- **LV_KEY_RIGHT/UP** - Go to toggled state if toggling is enabled.
-- **LV_KEY_LEFT/DOWN** - Go to non-toggled state if toggling is enabled.
+If `LV_OBJ_FLAG_CHECKABLE` is enabled `LV_KEY_RIGHT` and `LV_KEY_UP` makes the object checked, and `LV_KEY_LEFT` and `LV_KEY_DOWN` makes it unchecked.
 
 Note that, the state of `LV_KEY_ENTER` is translated to `LV_EVENT_PRESSED/PRESSING/RELEASED` etc.