table render hook: add Inner method

[jmooring]

Currently, if all you want to do is wrap a table with a div, you have to do this:

<div class="overflow-x-auto">
  <table
    {{- range $k, $v := .Attributes }}
      {{- if $v }}
        {{- printf " %s=%q" $k $v | safeHTMLAttr }}
      {{- end }}
    {{- end }}>
    <thead>
      {{- range .THead }}
        <tr>
          {{- range . }}
            <th
              {{- with .Alignment }}
                {{- printf " style=%q" (printf "text-align: %s" .) | safeHTMLAttr }}
              {{- end -}}
            >
              {{- .Text -}}
            </th>
          {{- end }}
        </tr>
      {{- end }}
    </thead>
    <tbody>
      {{- range .TBody }}
        <tr>
          {{- range . }}
            <td
              {{- with .Alignment }}
                {{- printf " style=%q" (printf "text-align: %s" .) | safeHTMLAttr }}
              {{- end -}}
            >
              {{- .Text -}}
            </td>
          {{- end }}
        </tr>
      {{- end }}
    </tbody>
  </table>
</div>

It would be convenient if we could do this instead:

<div class="overflow-x-auto">
  {{ .Inner }}
</div>

[jmooring]

I wrote this while thinking about a render hook for the docs site, but when I actually implemented it I realized that I wanted to replace the inline alignment styles with classes, so I wouldn't have used .Inner anyway.

So... this should have a very low priority. No one else has ever asked for it.