make type-or-section more obvious

It took me a long time to realize that /layouts/TYPE or SECTION/LAYOUT.html  was supposed to be a single URL and not two urls (/layouts/TYPE) or (SECTION/LAYOUT.html) ... putting in the hyphens I think makes it much more clear it's all one URL, and only the middle part is an either-or.
update docs for permalinks with all fields

List all the fields and what they mean, based on hugolib/permalinks.go