Add parse rule option

[kamiazya]

What was a problem

It was not possible to specify which object in the DOT language to parse.

How this PR fixes the problem

Add rule option for function parse.

import { Node } from 'ts-graphviz';
import { parse } from '@ts-graphviz/parser';

const node = parse(
  `test [
    style=filled;
    color=lightgrey;
    label = "example #1";
  ];`,
  { rule: 'node' },
);

console.log(node instanceof Node);
// true

Add rule option for function AST.parse .

import { AST } from '@ts-graphviz/parser';

const ast = AST.parse(
  `test [
    style=filled;
    color=lightgrey;
    label = "example #1";
  ];`,
  { rule: 'node' },
);

console.log(ast);
// {
//   type: 'node',
//   id: 'test',
//   attributes: [
//     { key: 'style', value: 'filled' },
//     { key: 'color', value: 'lightgrey' },
//     { key: 'label', value: 'example #1' }
//   ]
// }

Check lists (check x in [ ] of list items)

• Test passed
• Coding style (indentation, etc)