docs: bring back flat widget directory structure

docs/widgets/bar.md

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+# Bar (lv_bar)
+
+## Overview
+
+The bar object has a background and an indicator on it. The width of the indicator is set according to the current value of the bar.
+
+Vertical bars can be created if the width of the object is smaller than its height.
+
+Not only the end, but also the start value of the bar can be set, which changes the start position of the indicator.
+
+
+## Parts and Styles
+- `LV_PART_MAIN` The background of the bar and it uses the typical background style properties. Adding padding makes the indicator smaller or larger. The `anim_time` style property sets the animation time if the values set with `LV_ANIM_ON`.
+- `LV_PART_INDICATOR` The indicator itself; also uses all the typical background properties.
+
+## Usage
+
+### Value and range
+A new value can be set by `lv_bar_set_value(bar, new_value, LV_ANIM_ON/OFF)`.
+The value is interpreted in a range (minimum and maximum values) which can be modified with `lv_bar_set_range(bar, min, max)`.
+The default range is 0..100.
+
+The new value in `lv_bar_set_value` can be set with or without an animation depending on the last parameter (`LV_ANIM_ON/OFF`).
+
+### Modes
+The bar can be one of the following modes:
+- `LV_BAR_MODE_NORMAL` A normal bar as described above
+- `LV_BAR_MODE_SYMMETRICAL` Draw the indicator from the zero value to current value. Requires a negative minimum range and positive maximum range.
+- `LV_BAR_MODE_RANGE` Allows setting the start value too by `lv_bar_set_start_value(bar, new_value, LV_ANIM_ON/OFF)`. The start value always has to be smaller than the end value.
+
+## Events
+- `LV_EVENT_DRAW_PART_BEGIN` and `LV_EVENT_DRAW_PART_END` are sent for the following parts:
+    - `LV_BAR_DRAW_PART_INDICATOR` The indicator of the bar
+        - `part`: `LV_PART_INDICATOR`
+        - `draw_area`: area of the indicator
+        - `rect_dsc`
+
+See the events of the [Base object](/widgets/obj) too.
+
+Learn more about [Events](/overview/event).
+
+## Keys
+No *Keys* are processed by the object type.
+
+Learn more about [Keys](/overview/indev).
+
+## Example
+
+```eval_rst
+
+.. include:: ../../../examples/widgets/bar/index.rst
+
+```
+
+## API
+
+```eval_rst
+
+.. doxygenfile:: lv_bar.h
+  :project: lvgl
+
+```