Add support of relative Markdown links #56
Description
Examples:
[link to `foo.md` file](foo)
[link to `bar.md` file](foo.md)
[link to `baz.js` file](baz.js)
[link to Heading in this file](#heading){{ message }}
Examples:
[link to `foo.md` file](foo)
[link to `bar.md` file](foo.md)
[link to `baz.js` file](baz.js)
[link to Heading in this file](#heading)