Merge pull request #130 from ericshulman/master

Initial implementation of HTML5 Download Saving
Merge pull request #131 from ericshulman/master

improve messaging/interaction for fallback (download/manual) file saving
Merge pull request #133 from ericshulman/master

move download/saving message display to higher level
and fix TiddlySpace external JS beta links
Merge pull request #134 from ericshulman/master

update version/date for TW280 release
Merge pull request #138 from ericshulman/master

fixes for download saving: doctype, base64-encoding, messages
(note: also, bump version/date for TW281b1