Feature request: allow multi-select

[GoogleCodeExporter]

First off: thanks for this great plugin.

I've got an idea for a feature, and if I can grok the JS, i'll submit a patch.

Currently, all select elements render as single-select items, even when size is 
greater than 1.

I would love to be able to have a config option to allow multiple-select of 
options.

So, for example, if the tree looks like:
"Option 1": {"Suboption":200},
       "Option 2": {"Suboption 2": {"Subsub 1":201, "Subsub 2":202},
                "Suboption 3": {"Subsub 3":203, "Subsub 4":204, "Subsub 5":205}
               }

Then, shift-selecting "Option 1" and "Option 2" would cause "Suboption",  
"Suboption 2", and "Suboption 3" to appear together in a select element 
(instead of just "Suboption" or "Suboption 2 and Suboption 3").

Original issue reported on code.google.com by [email protected] on 28 Nov 2011 at 9:02