Multisite support

• Multisite support (!)
• A new operation mode: "No conversion", if you do not want to use WebP Express for converting. Replaces the old "Just redirect" mode
• Added capability testing of .htaccess. The .htaccess rules are now tailored to the capabilities on the system. For example, on some platforms the filename of a requested image is passed to the converter script through the query string, but on platforms that supports passing it through an environment variable, that method is used instead
• Picturefill.js is now optional (alter html, picture tag)
• A great bunch more!