Sage 9.0.0-beta.4

• Update to Bootstrap 4.0.0-beta (#1943)
• PHP 7+ is now required (#1935)
• Update dependencies, support config-local.json, implement autoload system for styles/scripts, use roots/sage-installer, use roots/sage-lib (#1919)
• Add soberwp/controller (#1903)
• Change syntax of template call to match other files in views (#1908)
• Add Tachyons as a CSS framework option (#1867)
• Remove post format reference in template call (#1904)
• Update inline documentation to reflect correct theme file locations (#1890)
• Optimize CSS Assets safe = true (#1901)
• Update Autoprefixer and standardize browserlist location (#1899)
• Do not redirect for WP-CLI (#1891)
• Illuminate: container make with parameters (#1888)
• Add Stylelint for linting stylesheets (#1885)