Use $(...) to delimit the generated hash

[ignatiusmb]

Is your feature request related to a problem? Please describe.
When writing headings, it would be nice if we can indicate a way for the parser to generate a hash from a selected range instead of the whole heading.

Describe the solution you'd like
Add a delimiter $(...) that can be used inside the headings, such that we can get #hello-world from the following markdown

## 1 / 2 / 3 | $(hello world)

Describe alternatives you've considered
Use brackets [...] but that would conflict with links and images, and would be harder to use literally with escaping and such.