add utf8 library docs

doc/en/scripting.md

@@ -21,6 +21,7 @@ Subsections:
     - [player](scripting/builtins/libplayer.md)
     - [quat](scripting/builtins/libquat.md)
     - [time](scripting/builtins/libtime.md)
+    - [utf8](scripting/builtins/libutf8.md)
     - [vec2, vec3, vec4](scripting/builtins/libvecn.md)
     - [world](scripting/builtins/libworld.md)
 - [Module core:bit_converter](scripting/modules/core_bit_converter.md)

doc/en/scripting/builtins/libutf8.md

@@ -0,0 +1,18 @@
+# *utf8* library
+
+The library provides functions for working with UTF-8.
+
+```lua
+-- Converts a UTF-8 string to a Bytearray or an array of numbers if
+-- the second argument is true
+utf8.tobytes(text: str, [optional] usetable=false) -> Bytearray|table
+
+-- Converts a Bytearray or an array of numbers to a UTF-8 string
+utf8.tostring(bytes: Bytearray|table) -> str
+
+-- Returns the length of a Unicode string
+utf8.length(text: str) -> int
+
+-- Returns the code of the first character of the string
+utf8.codepoint(chars: str) -> int
+```

doc/ru/scripting.md

@@ -21,6 +21,7 @@
     - [player](scripting/builtins/libplayer.md)
     - [quat](scripting/builtins/libquat.md)
     - [time](scripting/builtins/libtime.md)
+    - [utf8](scripting/builtins/libutf8.md)
     - [vec2, vec3, vec4](scripting/builtins/libvecn.md)
     - [world](scripting/builtins/libworld.md)
 - [Модуль core:bit_converter](scripting/modules/core_bit_converter.md)

doc/ru/scripting/builtins/libutf8.md

@@ -0,0 +1,18 @@
+# Библиотека *utf8*
+
+Библиотека предоставляет функции для работы с UTF-8.
+
+```lua
+-- Конвертирует UTF-8 строку в Bytearray или массив чисел если
+-- второй аргумент - true
+utf8.tobytes(text: str, [опционально] usetable=false) -> Bytearray|table
+
+-- Конвертирует Bytearray или массив чисел в UTF-8 строку
+utf8.tostring(bytes: Bytearray|table) -> str
+
+-- Возвращает длину юникод-строки
+utf8.length(text: str) -> int
+
+-- Возвращает код первого символа строки
+utf8.codepoint(chars: str) -> int
+```