Plans to allow regex for dynamic params?

Hello!

Thanks for creating `matchit`, it's simple and clean.

I am checking to see if you will accept a PR, which allows the support for regex for dynamic parameters. For example:

```js
parse('/user/:id', {
id: '[0-9]+'
})
```

Unlike `path-to-regexp`, this change will not allow regex with in the pattern. However, one can define it just for the dynamic parameters.

I am happy to share a Pull request for same, but wanted to know, if you would like to have this as an addition or not?

No implementation files, tests, or entry points are named. Review the existing parse API and its documentation first, then determine how dynamic-parameter regex options should be specified and tested; done means the example pattern accepts numeric ids without allowing regex directly in the route pattern.

Written by the indexing model from the issue text.