module File: File
type 
This type represents a file in the filesystem that is your site.
val of_html : name:string -> Html.t -> t
Specify that there ought to be a file with the given name containing
    the given HTML.
val of_path : ?name:string -> string -> t
Specify that there ought to be a copy of the file at the given path
    with the given name. If no name is provided the basename of the path
    will be used.
val build : t -> in_directory:string -> unit Async.Std.Deferred.t
Instantiates the file specification in the given directory. You should
    not typically need to call this directly and instead should just use
    Site.build which calls this.