A few documentation improvements for `syntax::print::pp`
A few documentation improvements for `syntax::print::pp`

* Moved algorithm explanation to module docs
* Added ``` before and after the examples
* Explanation of the `rbox`, `ibox` and `cbox` names
* Added docs about the breaking types to `Breaks`

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