Can't include file with spaces in name

[Evian-Zhang]

I found issue Files with spaces are not found #527, which I had exactly the same problem.

I have a file name with space.md, and I want to include this file in SUMMARY.md as:

- [name with sapce](./name with space.md)

and then I used mdbook build, and failed with

2020-07-26 10:06:23 [WARN] (mdbook::book::summary): Expected a start of a link, actually got Some(Text(Borrowed("[")))
2020-07-26 10:06:23 [ERROR] (mdbook::utils): Error: Summary parsing failed
2020-07-26 10:06:23 [ERROR] (mdbook::utils): 	Caused By: There was an error parsing the numbered chapters
2020-07-26 10:06:23 [ERROR] (mdbook::utils): 	Caused By: There was an error parsing the numbered chapters
2020-07-26 10:06:23 [ERROR] (mdbook::utils): 	Caused By: failed to parse SUMMARY.md line 4, column 3: The link items for nested chapters must only contain a hyperlink

I have tried:

- [name with sapce]("./name with space.md")
- [name with sapce](./name+with+space.md)
- [name with sapce](./name%20with%20space.md)
- [name with sapce](./name\ with\ space.md)

as suggested in the issue #527, but none of those approaches succeeded. Method 1 and 4 failed with the same output, method 2 and 3 created a dummy name+with+space.md or name%20with%20space.md file, and the output html does not contain the content in my name with space.md.

I am working on macOS 10.15, with mdbook v0.4.1

[magicdmer]

I meet the same problem , use win32 lastest relase，example：
[test](./test protocol.md)