Modified Exhibit.getAttribute to use .attr() instead of .data()
jquery's .data() method polls data-* attributes from the tag only
once, then caches them.  So changes to the attributes (for example,
while editing the exhibit) will not be reflected in later calls to
.data().  Also, the .data() method attempts to parse the value of the
attribute and return an appropriate number, object, or array while
Exhibit.getAttribute is used in code that expects to get strings and
do its own conversion.
tidied code
Updated modularity and caching in the cloud facet.  At some point in
the past, modularity of list facet was improved, and caching was
added, but the cloud facet did not go through the same process.  Since
cloud facet code is almost identical to list facet, it was easy to
carry over the changes.  Longer term, the common code between list and
cloud facets should be merged.
remove unused code and variables
Release document.
Update RELEASES.txt
Revised large-data demo to use more facets.
Merge pull request #51 from karger/2013-10-15_data_attr

Modified Exhibit.getAttribute to use .attr("data-...") instead of .data()
Merge pull request #55 from karger/2013-10-20_cloud

2013 10 20 cloud
Merge pull request #58 from karger/2013-10-22_big_demo

Revised large-data demo to use more facets.