feature request: inline comments

[nekomeowww]

While #4 is trying to implement a commenting system aside of elements of block level, it is not possible to be able to cover every need for comments, I suggest implementing an inline comments integration for comments inside of the lines with <mark></mark> elements or similar approaches.

Subjective thinking: we benefit from the overall UI/UX of footnote integrations and context connecting, author notes can be improved significantly since footnote is context-less and breaking reading experiences which will eventually violates my guidelines of documentation writing and best practice of documentation organization.