baseUrl's value sometimes wrong when referencing inner website's content

[yamgent]

What is the purpose of this pull request? (put "X" next to an item, remove the rest)

• [X] Bug fix

Fixes #262.

What is the rationale for this request?
When including files belonging to an inner website, the computation of baseUrl is wrong if the depth of the inclusion is only 1.

What changes did you make? (Give an overview)
Fixed the logic of the algorithm such that the computation of baseUrl is correct regardless of how deep the inclusion is.

Provide some example code that this change will affect:
https://github.com/yamgent/markbind-problems/tree/master/issue_262

Is there anything you'd like reviewers to focus on?
The soundness of the fix.

Testing instructions:

1. Clone https://github.com/yamgent/markbind-problems.git.
2. Go to issue_262 directory.
3. Run markbind serve.
4. Everything should render with This is cheese's baseUrl: /main_website/inner_site.
   a. In the buggy version, the first entry will show This is cheese's baseUrl: /main_website.

[yamgent]

Additional writeup:

This is the content that MarkBind generates, before it processes the includes through result => markbinder.resolveBaseUrl(result, fileConfig):

---

# 262: Broken baseUrl links for inner websites

Version: v1.8.0.

## Include `inner_site/cheese.md`:
<div cwf="C:\Users\Tan Wang Leng\Documents\GitHub\yamgent\markbind-problems\issue_262\index.md" include-path="C:\Users\Tan Wang Leng\Documents\GitHub\yamgent\markbind-problems\issue_262\inner_site\cheese.md">

This is cheese's baseUrl: {{baseUrl}}.

</div>

## Include `inner_site/index.md`:
<div cwf="C:\Users\Tan Wang Leng\Documents\GitHub\yamgent\markbind-problems\issue_262\index.md" include-path="C:\Users\Tan Wang Leng\Documents\GitHub\yamgent\markbind-problems\issue_262\inner_site\index.md">

<div cwf="C:\Users\Tan Wang Leng\Documents\GitHub\yamgent\markbind-problems\issue_262\inner_site\index.md" include-path="C:\Users\Tan Wang Leng\Documents\GitHub\yamgent\markbind-problems\issue_262\inner_site\cheese.md">

This is cheese's baseUrl: {{baseUrl}}.

</div>

</div>

## Expected correct rendering
This is cheese's baseUrl: /main_website/inner_site.

---

The first {{baseUrl}} generates the wrong URL, while the second {{baseUrl}} is correct.

This is because:

1. cwf, rather than the include-path, is used to determine if the content belongs from an inner website.
2. If the depth of the include is not at least 2, then whether we use cwf or include-path to determine 1. does not matter, because it is not processed anyway.

Hence, my PR fixes the two problems mentioned above.

[yamgent]

@acjh if you have the time, do feel free to take a look at the PR. :)

[yamgent]

@nicholaschuayunzhi @acjh Just a heads up, will be getting this merged tomorrow morning, feel free to review this whenever you can. :)