Spec gotcha: directory entry must end with `/`

SourceItem specifies that a directory entry must end with /. This is a detail that is likely to be missed by implementors of the spec, both client and server and requires looking at the string to determine if something is a directory. I suggest making it an explicit field in SourceItem (and probably DependencySourceItem as well.

trait SourceItem {
  /** Either a text document or a directory. A directory entry must end with a forward
    * slash "/" and a directory entry implies that every nested text document within the 
    * directory belongs to this source item.
    */
  def uri: Uri

  /** Indicates if this source is automatically generated by the build and is not
    * intended to be manually edited by the user. */
  def generated: Boolean
}

[olafurpg]

Sounds good, if you open a PR I’m happy to LGTM 👍

[jastice]

Solved via #83