port lastest style changes from upstream
set Asciidoctor 1.5.0 free!

- upgrade site to Asciidoctor 1.5.0
- publish 1.5.0 release annoucement
- sync index page with Asciidoctor README
- update man asciidoctor(1) page
- update styles from upstream
Set publish date of post news/asciidoctor-1-5-0-released.adoc [ci skip]
remove italics from post title
properly title the awesome-est song
take participant names out of table to be nicer to mobile
update syntax quickref pdf
link to Sarah's GitHub page
minor edit
reorder points in XHTML section
fix link to 1.5.0 release notes
revisions to migration guide
add link to DocGist from navigation bar
Update installation requirements for Asciidoctor 1.5.0
add revremark to initial final version
credit Anton Moiseev for AsciiDoc language support for Atom
Credit Anthonny and Peter in Asciidoctor 1.5.0 announcement
add new document with asciidoctorj 1.5.0 release notes.
updates manual with new additions.
copyedits