Rewrite without regex crate.
The regex approach was broken. If the following _content_ was provided
in the entry:
foo
---
bar
The regex approach parsed the header until the "---" in the content.
This is, of course, not the way to do that.
Now, the parsing is implemented by hand. Should be faster as well,
though I don't care about this.
This fixes a severe bug.
Matthias Beyer
9fb5f453fe