TRPL: Fix Headlines, Links in "Error Handling"
TRPL: Fix Headlines, Links in "Error Handling"

- Headlines begin at 1st level now like the rest of the book
- All Headlines a blank line above and below
- Fix links in this chapter's TOC

GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust