apply doc improvements from 2.1

<directivesynopsis>

<name>AddDefaultCharset</name>

<description>Default charset parameter to be added when a response

content-type is "text/plain" or "text/html"</description>

content-type is <code>text/plain</code> or <code>text/html</code></description>

<syntax>AddDefaultCharset On|Off|<var>charset</var></syntax>

<default>AddDefaultCharset Off</default>

<contextlist><context>server config</context>

    <p>This directive specifies a default value for the media type

    charset parameter (the name of a character encoding) to be added

    to a response if and only if the response's content-type is either

    "text/plain" or "text/html".  This should override any charset

    specified in the body of the document via a <code>META</code> tag,

    though the exact behavior is often dependent on the user's client

    <code>text/plain</code> or <code>text/html</code>.  This should override

    any charset specified in the body of the response via a <code>META</code>

    element, though the exact behavior is often dependent on the user's client

    configuration. A setting of <code>AddDefaultCharset Off</code>

    disables this functionality. <code>AddDefaultCharset On</code> enables

    a default charset of <code>iso-8859-1</code>. Any other value is assumed

      AddDefaultCharset utf-8

    </example>

    <p><code>AddDefaultCharset</code> should only be used when all

    <p><directive>AddDefaultCharset</directive> should only be used when all

    of the text resources to which it applies are known to be in that

    character encoding and it is too inconvenient to label their charset

    individually. One such example is to add the charset parameter