Does not support multiple enclosures

[TingPing]

If you have an item such as;

<item>
    <enclosure sparkle:os="windows-x86" />
    <enclosure sparkle:os="windows-x64" />
</item>

It will always overwrite the values with the last enclosure. It could store a list of these enclosures or maybe only store the first enclosure that is for the correct platform.

[vslavik]

Related: #50.

Yes, the best matching enclosure should be used, and the check for <item>’s suitability should consider all enclosures.