add the md files from the docs repo to start updating them to v8

docs/widgets/calendar.md

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+```eval_rst
+.. include:: /header.rst 
+:github_url: |github_link_base|/widgets/calendar.md
+```
+# Calendar (lv_calendar)
+
+## Overview
+
+The Calendar object is a classic calendar which can:
+- highlight the current day
+- highlight any user-defined dates
+- display the name of the days
+- go the next/previous month by button click
+- highlight the clicked day
+
+
+## Parts and Styles
+The calendar's main part is called `LV_CALENDAR_PART_BG`. It draws a background using the typical background style properties.
+
+Besides the following virtual parts exist:
+- `LV_CALENDAR_PART_HEADER` The upper area where the current year and month's name is shown. It also has buttons to move the next/previous month. 
+It uses typical background properties plus padding to adjust its size and margin to set the distance from the top of the calendar and the day names below it.
+- `LV_CALENDAR_PART_DAY_NAMES` Shows the name of the days below the header. It uses the *text* style properties padding to keep some distance from the background (left, right), header (top) and dates (bottom).
+- `LV_CALENDAR_PART_DATES` Show the date numbers from 1..28/29/30/31 (depending on current month). Different "state" of the states are drawn according to the states defined in this part:
+  - normal dates: drawn with `LV_STATE_DEFAULT` style
+  - pressed date: drawn with `LV_STATE_PRESSED` style
+  - today: drawn with `LV_STATE_FOCUSED` style
+  - highlighted dates: drawn with `LV_STATE_CHECKED` style   
+
+
+## Usage
+
+
+## Overview
+
+To set and get dates in the calendar, the `lv_calendar_date_t` type is used which is a structure with `year`, `month` and `day` fields.
+
+
+### Current date
+To set the current date (today), use the `lv_calendar_set_today_date(calendar, &today_date)` function.
+
+### Shown date
+To set the shown date, use `lv_calendar_set_shown_date(calendar, &shown_date)`;
+
+### Highlighted days
+The list of highlighted dates should be stored in a `lv_calendar_date_t` array loaded by `lv_calendar_set_highlighted_dates(calendar, &highlighted_dates)`.  
+Only the arrays pointer will be saved so the array should be a static or global variable.
+
+### Name of the days
+The name of the days can be adjusted with `lv_calendar_set_day_names(calendar, day_names)` where `day_names` looks like `const char * day_names[7] = {"Su", "Mo", ...};`
+
+### Name of the months
+Similarly to `day_names`, the name of the month can be set with `lv_calendar_set_month_names(calendar, month_names_array)`.
+
+## Events
+Besides the [Generic events](../overview/event.html#generic-events), the following [Special events](../overview/event.html#special-events) are sent by the calendars:
+**LV_EVENT_VALUE_CHANGED** is sent when the current month has changed.
+
+In *Input device related* events, `lv_calendar_get_pressed_date(calendar)` tells which day is currently being pressed or return `NULL` if no date is pressed.
+
+## Keys
+No *Keys* are processed by the object type.
+
+Learn more about [Keys](/overview/indev).
+
+
+## Example
+
+```eval_rst
+
+.. include:: /lv_examples/src/lv_ex_widgets/lv_ex_calendar/index.rst
+
+```
+
+## API
+
+```eval_rst
+
+.. doxygenfile:: lv_calendar.h
+  :project: lvgl
+
+```