Revise features, keyboard, and states/properties for File Directory T…

…reeview Example Using Declared Properties

For issue #224, modified examples/treeview/treeview-1/treeview-1b.html:
* removed redundant information about computed level, setsize, and posinset from accessibility features section.
* Added summary of treeview terminology with link to pattern.
* Revisions for editorial consistency to keyboard table.
* Updated states/properties section header.
* Revisions for editorial consistency to states and properties table.