fix:Allow supply any character as bullet in lists

[xmagor]

To allow defined specific character, either literally or as a Unicode escape
sequence.

For example taken from list reportlab examples:

    <ul>
        <li value="&#x2022;"><para style="normal">Bullet, defined by unicode code point</para></li>
    </ul>

[regebro]

Thanks for raising this issue. This is not the correct solution, as this would allow any 1 character text in any Choice field, but I have made a PR that fixes this: #113 I have to verify the Reportlab behavior before merging this, though.

Thanks again!