XML minifier incorrectly un-escapes numeric entities

[picasticks]

Sorry I don't have a PR for this, but it appears to only affect the XML minifier, not HTML, so you may just want to add a RevEntitiesMap for XML to pass to the parser.

Named entities work fine, only numeric entities are un-escaped.

Quick way to replicate the issue:

$ echo '<title>Test &amp; &lt; &#038; &#60; XML</title>' | minify --mime application/xml
<title>Test &amp; &lt; & < XML</title>

Instead of returning something like:

<title>Test &amp; &lt; &#38; &#60; XML</title>

Or:

<title>Test &amp; &lt; &amp; &lt; XML</title>

For context, this came up for me because Minify broke a WordPress-generated RSS feed. WordPress escapes & with the numeric entity & (including one leading 0). So, that's one data point on how often & is being used instead of &.