0.1.0-alpha025

Changed the type XmlAttribute from the XmlViewEngine to accept either a string * string key value pair or a boolean attribute of type string. This was a missing to enable script tags such as <script src="..." async></script>.

Added two helper functions (attr and flag) to simplify the creation of those attributes:

script [
    attr "src" "http://example.org/example.js"
    attr "lang" "javascript"
    flag "async" ] []