Don't use &amp;, &lt; and &gt; for escaping &, < and >

[mibe]

The XML spec. clearly states that these chars have to be escaped, and FeedWriter does that. But the RSS Best Practices recommends using the hexadecimal character reference:

A publisher should encode "&" and "<" in plain text using hexadecimal character references. When encoding the ">" character, a publisher should use the hexadecimal reference >.

This maximizes the compatibility with clients.