doc/source/format.rst: Some enhancements in how we document dependencies

 * Added link target in the project.conf documentation for the element-path

 * List elements in examples without the leading `elements/` path, this
   is misleading and predates the existence of the element-path

 * Specify "element path relative" instead of "project relative", this
   was also outdated. Use these opportunities to link back to the element
   path project.conf docs section

 * Document dependency attributes differently

   - Use a list of attributes

   - Link back to the first example when speaking of shorthand, instead
     of duplication the example in two places

   - Enhanced description of how junction attributes are used

   - Note that ordering in dependency declaration lists is not meaningful

     This is an incorporation of Javier Jardón's patch for issue #358

This fixes issue #358.