Fix loads of asciidoc errors
Fix asciidoctor syntax problems and updgrade to asciidoctor 1.5

Points to note for authors:

* Nesting "*" in `literals` does not behave like Markdown - you have to
escape the asterisk (e.g. `foo/\*`)

* Quote ligatures (why we had to use those I don't really know) are
different in asciidoctor 1.5 ('`foo`' instead of ``foo'')

Merge branch '1.1.x'

Conflicts:
	spring-boot-docs/src/main/asciidoc/production-ready-features.adoc
	spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc