HTML element attributes on template call

Setting HTML element attributes is supported for calls to built-in templates, the syntax is as follows:

templatename(...)[attrname=e, ...]{ ... }

attrname is an attribute name, and e is a webdsl expression such as "foo" or "foo"+bar.

Example:

define page root(){ 
  var somevalue := "lo"
  image("/images/logosmall.png")[alt = somevalue+"go", longdesc = "blablabla"]
  navigate root()[title = "root page"]{ "root" }
}