[Groff] better .DS/.DE & friends for -Thtml

[Dorai Sitaram]

groff -Thtml currently converts .DS/.DE and all its
variants into <pre>...</pre>.

One can use <div>, <table>, <br>, and &nbsp; to get 
a translation that is more true to the intent. 
.DS/.DE should ideally only affect spaces,
end-of-lines, individual line adjustment, and overall
display adjustment.  The font should not be changed to
monospace (unless the user requests it by an explicit
command).

I am enclosing the HTML translations for all the
.DS variants.  In the following, all spaces in
content[123] are translated to &nbsp;, in all the
variants.



.DS L    \" or .LD
content1
content2
content3
.DE

=>

<div align=left>
<table>
<tr>
<td align=left>
content1<br>
content2<br>
content3<br>
</td>
</tr>
</table>
</div>

***************************************************************

.DS I    \" or .ID
content1
content2
content3
.DE

=>

<div align=left>
<table>
<tr>
<td width="8%">&nbsp;</td>
<td align=left>
content1<br>
content2<br>
content3<br>
</td>
</tr>
</table>
</div>

***************************************************************

.DS C    \" or .CD
content1
content2
content3
.DE

=>

<div align=center>
<table>
<tr>
<td align=center>
content1<br>
content2<br>
content3<br>
</td>
</tr>
</table>
</div>

***************************************************************

.DS B    \" or .BD
content1
content2
content3
.DE

=>

<div align=center>
<table>
<tr>
<td align=left>
content1<br>
content2<br>
content3<br>
</td>
</tr>
</table>
</div>

***************************************************************

.DS R    \" or .RD
content1
content2
content3
.DE

=>

<div align=right>
<table>
<tr>
<td align=right>
content1<br>
content2<br>
content3<br>
</td>
</tr>
</table>
</div>