EXPERIMENTAL: supporting asciidoctor configuration files

• Update to AsciidoctorJ 1.5.8.1
• Workaround for incompatible plugins (#226)
• Toggle softwraps only available in context menu of AsciiDoc documents (#227)
• Recognize list continuations plus block instead of marking them as old style headings (#228)
• EXPERIMENTAL: supporting .asciidoctorconfig configuration files

See Wiki Page on configuration files for more information.