releases 1.5 documentation updates and edits

- converters
- substitutions
- include and tag directives
- stem
- migrates monospace syntax for several sections
- edits release blog and release notes
- fixes broken sections in user manual
Merge pull request #251 from graphitefriction/1-5-release-notes

releases 1.5 documentation updates and edits
add FIXME to not set pub date in pull request
reenable compressed styles
fix top margin on secondary content
docs for pass, xref, and url
Merge pull request #252 from graphitefriction/1-5-release-notes

docs for pass, xref, and url
copyedits
Merge pull request #253 from graphitefriction/1-5-release-notes

copyedits
fix source listings in load-render-api doc
revisions to 1.5.0 release notes & announcement; update screenshots
Set publish date of post news/asciidoctor-1-5-0-released.adoc [ci skip]