Files/directories with spaces in names don't link properly

[dmoles]

Steps to reproduce:

1. in a new repo, create a couple of Markdown files and/or subdirectories with spaces in their names
2. either:
   • create a README linking to those files/subdirectories, or
   • don't create a README and use the auto TOC instead
3. start adler with this directory as the root
4. view the adler root page

Expected:

• files and subdirectories are rendered as links

Actual:

• links are rendered as [text](href)