Fixed a number of places where the validation was incorrect:
  1)  Used to require the "Required if Available" fields.  Now there is a checkbox to require this
  2)  Added a checkbox to require extended fields if required.
  3)  Fixed a number of properties that were a little wrong, e.g. keywords should be keyword.
  4)  Fixed a number of the formats.  E.g. issued + modified require date not datetime.
Fixed up the markdown to include instructions on running locally.
Fixed some formatting issues
Merge pull request #6 from willpugh/gh-pages

Fixed a bunch of bugs, and some documentation issues