Issue 3190: Fix W3C compliance.

Issue 3190: Fix W3C compliance.

Fix incorrect nesting of tables in `Manuals' section of
  Community > Development on website.

Adjust css rules as needed.

[Mark Polesky, 2013-06-29 02:48:53]

Issue 3190 lists 2 separate problems, w3c compliance and lynx compatibility:
http://code.google.com/p/lilypond/issues/detail?id=3190

I've fixed the w3c compliance problem, though I haven't checked the lynx
problem.  If the lynx thing is still problematic, someone should open a new
issue for that.

Adding extra @multitable's was the way to go; the misaligned columns were easily
solved by explicitly giving widths to the tables in css.  In the future, if a
new manual link ever gets added with a name too long to fit, it is trivial to
adjust the css rule.

There was another option of using:
@multitable {dummy text to space col 1} {same for col 2}, etc.

...but I chose to take the css route.

One last thing, another patch I posted early today edits the same file,
Documentation/css/lilypond-website.css
(https://codereview.appspot.com/10700044/).  I don't know if a rebase will be
needed or what, just thought I'd mention it.

Feel free to check this.

Thanks.
- Mark

[Graham Percival, 2013-07-02 23:35:15]

LGTM.

The "lynx issue" looks bogus to me.  AFAIK relative links are completely allowed
in html.