Add clarification about output path of asset files
`layout` defaults to `none` (`nil`)
Tweak wording about assets
Merge pull request #2078 from ZDroid/rm-layout-none

Remove redundant `layout: none`
Sanitize paths uniformly, in a Windows-friendly way.

Fixes kinda a #1948 thing.
Related to #1946.
Merge pull request #2065 from jekyll/fix-windows-root-system-thingy
Update history to reflect merge of #2065 [ci skip]
Merge pull request #2067 from troyswanson/assets-can-be-better
Update history to reflect merge of #2067 [ci skip]