feat(macro): add $seq method

help/FEATURES.md

@@ -641,6 +641,7 @@ If the expression needs to contain [\= or =\], please enter `[\=` or `=\]` to es
 - application version: [= $ctx.version =]
 - current document name: [= $doc.basename =]
 - current time:  [= $ctx.lib.dayjs().format('YYYY-MM-DD HH:mm') =]
+- sequence: [= $seq`Figure-` =] | [= $seq`Figure-` =] | [= $seq`Figure-` =] | [= $seq`Table-` =] | [= $seq`Table-` =]
 - qualifier escape:  [= '[\= =\]' =]
 - Arithmetic:  [= (1 + 2) / 2 =]
 - reference file (support 3 levels of nesting, you can use Front Matter variable defined in the target document):
@@ -680,6 +681,7 @@ variable name | type | description
 `$afterMacro` | `(fn: (src: string) => string) => Result` | Define a macro-replaced callback function that can be used for further processing of the replaced text.
 `$noop` | `() => Result` | no operation, Used for holding text space
 `$doc` | `object` | Current document information
+`$seq` | `(label: string) => Result` | Sequence
 `$doc.basename` | `string` | File name of current document (no suffix)
 `$doc.name` | `string` | File name of current document
 `$doc.path` | `string` | Current document path

help/FEATURES_ZH-CN.md

@@ -641,6 +641,7 @@ Front Matter 中的 `define` 字段可以定义一些文本替换映射。支持
 - 应用版本：[= $ctx.version =]
 - 当前文档名: [= $doc.basename =]
 - 当前时间: [= $ctx.lib.dayjs().format('YYYY-MM-DD HH:mm') =]
+- 计数器: [= $seq`图-` =] | [= $seq`图-` =] | [= $seq`图-` =] | [= $seq`表-` =] | [= $seq`表-` =]
 - 限定符转义: [= '[\= =\]' =]
 - 四则运算: [= (1 + 2) / 2 =]
 - 引用文件（支持最多嵌套 3 层，可使用目标文档中定义的 Front Matter 变量)
@@ -679,6 +680,7 @@ Front Matter 中的 `define` 字段可以定义一些文本替换映射。支持
 `$export` | `(key: string, val: any) => Result` | 定义一个本文档可以使用的变量
 `$noop` | `() => Result` | 无操作函数，可用于文本占位使用
 `$afterMacro` | `(fn: (src: string) => string) => Result` | 定义一个宏替换后的回调函数，可用于对替换后的文本进行进一步处理。
+`$seq` | `(label: string) => Result` | 文档内部计数器
 `$doc` | `object` | 当前文档信息
 `$doc.basename` | `string` | 当前文档文件名（无后缀）
 `$doc.name` | `string` | 当前文档文件名