Serializing FLOAT values does not work

Just so I don't forget, noticed this on the way. The simple patch looks like this:

``` diff
diff --git a/lib/ical/ical.js b/lib/ical/ical.js
index a5920b5..29014ed 100644
--- a/lib/ical/ical.js
+++ b/lib/ical/ical.js
@@ -599,9 +599,6 @@ ICAL.design = (function() {
},
float: {
matches: /^[+-]?\d+\.\d+$/,
- decorate: function(aValue) {
- return ICAL.Value.fromString(aValue, "float");
- },

fromICAL: function(aValue) {
var parsed = parseFloat(aValue);
```

Needs tests of course.

Start in lib/ical/ical.js at the FLOAT design entry, especially the shown decorate and fromICAL functions. Add focused tests for FLOAT serialization and run the relevant test suite; done means FLOAT values serialize successfully without the reported failure.

Written by the indexing model from the issue text.