Make abbreviations expand on quotes as well as space.

Also added rough documentation for insert mode.

TODO: Abbreviations should also expand on <CR> and <Tab>, but right now
adding <CR> to the mappings.add() has no effect, and adding <Tab> to the
mappings.add() breaks tab completion.

TODO: Rather than listing non-keyword characters in two places (ui.js
and mappings.js), they should be specified in one location (that could
someday be trumped by an 'iskeyword' option).

common/content/ui.js

@@ -878,8 +878,15 @@ function CommandLine() //{{{
         ["<C-c>"], "Focus content",
         function () { events.onEscape(); });
 
+    // Any "non-keyword" character triggers abbreviation expansion
+    // TODO: Add "<CR>" and "<Tab>" to this list
+    //       At the moment, adding "<Tab>" breaks tab completion. Adding
+    //       "<CR>" has no effect.
+    // TODO: Make non-keyword recognition smarter so that there need not
+    //       be two lists of the same characters (one here and a regexp in
+    //       mappings.js)
     mappings.add(myModes,
-        ["<Space>"], "Expand command line abbreviation",
+        ["<Space>", '"', "'"], "Expand command line abbreviation",
         function ()
         {
             commandline.resetCompletions();