[Feature Request] Support placeholder format keyword

[TenviLi]

Because of some problems, {title} often not equal to {h1_title}

should we support the new keyword {h1_title}?

---

and {relative_path} is so important

this new keyword can handle the result of {path} keyword and return the relative pathname without markdown filename.

if set the query:path: keyword, the result of {relative_path} will be cut down the substring (Is the value of query:path: you set)

here is a example

- docs
  - test
    - haha.md

if set the format:'s value as {relative_path} {title}, it will be rendered into

test haha

if set {path} {title}, it will be rendered into

docs/test/haha haha