add std::fmt

.vitepress/config.ts

@@ -372,6 +372,7 @@ export default defineConfig({
             },
             { text: 'std::env', link: '/standard-library/std-env' },
             { text: 'std::errors', link: '/standard-library/std-errors' },
+            { text: 'std::fmt', link: '/standard-library/std-fmt' },
             { 
               text: 'std::fs', 
               link: '/standard-library/std-fs', 

src/standard-library/std-fmt.md

@@ -0,0 +1,19 @@
+# std::fmt
+
+## Functions
+```jule
+fn format(fmt: str, args: ...any): str
+```
+It places the passes arguments in the string relative to the corresponding format string. The to_str function provided by the API is used for string conversion. Returns format string if `args.len == 0`. If the arguments have ended, the remaining part of format string is not processed and is returned as is.
+
+**Formatting:**
+
+Arguments are processed sequentially. That is, when an argument encounters a format string parameter, it will be processed according to how many parameters it is. The 5th parameter uses the 5th argument as the value.
+
+Each format parameter is represented as `{}` in the format string. These parameters will then be deleted according to the processing algorithm and replaced with arguments.
+
+**Examples:**
+
+- `format("{} {}!", "Hello", "World")` = `"Hello World!"`
+- `format("{} {}")` = `"{} {}"`
+- `format("{} is the {}", "PI Number")` = `"PI Number is the {}"`