0.6.0.alpha1

• Update to Ruby 2.4
• Ignore .htaccess in subdirectories (#541)
• Add support for Haml version 5 (#539)
• Correct logging of errors in partial (#518)
• Fix default number of threads for site generation (#523 )
• Fix generated gemfile for awestruct --init -f foundation (#521)
• Fix issue with Awestruct location in awestruct --init -f foundation (#519)
• Store Asciidoctor::Document object in page context (#288)
• Sitemap extension: changed default priority to 0.5 to match spec and docs (8700e20)