Handle '+' as space in URI (hound-search#313)

Traditional URI encoding uses '+' instead of '%20' to represent
spaces in URI parameters, but the decodeURIComponent method
does not recognize this representation.

This is significant because Chrome's "Manage Search Engines"
settings page, which lets users add arbitrary search engines
as shortcuts in that browser's location bar, represents spaces
using the '+' character. So, if you try to add a local Hound
instance to your Chrome search engines, any multi-word search
will be replaced by a weird regular expression, as the '+'
characters will be retained in the search box.

For instance, without this change, if you were to set 'hound'
as the shortcut term, then entering 'hound some thing' will
send the search parameter '?q=some+thing' to Hound, resulting
in a search for the regular expression /some+thing/, matching
'something', 'someething', 'someeeeeeeeething', etc.

Regular expression search is not affected by this change,
because an actual "+" character entered using this Chrome
feature will be encoded as %2B, and the '+' will appear in
Hound's search box correctly.

ui/assets/js/hound.js

@@ -60,6 +60,10 @@ var ParamsFromQueryString = function(qs, params) {
       return;
     }
 
+    // Handle classic '+' representation of spaces, such as is used
+    // when Hound is set up in Chrome's Search Engine Manager settings
+    pair[1] = pair[1].replace('+', ' ');
+
     params[decodeURIComponent(pair[0])] = decodeURIComponent(pair[1]);
   });