The %HTML.Forms directive enables Forms module regardless of the %HTML.Trusted
value. This adds support for form elements without enabling other unsafe
modules, such as Scripts, Iframe or Object.
To achieve the same effect without this directive one has to explicitly list
all enabled modules in %HTML.AllowedModules, and any not listed will be
removed. This however is not very convenient, as the allowed modules may vary
between doctypes.
Resolves#213.
