The meta plugin, when used to add a stylesheet to a page, adds the
following attributes by default:

  - `rel="alternate stylesheet"`
  - `title="mystylesheet"`

The intent of this feature, according to the documentation is to "add a
stylesheet to a page".

  - By setting the `rel="alternate stylesheet"`, the additional
    stylesheet is treated as an "alternate stylesheet" as described in
<http://www.w3.org/Style/Examples/007/alternatives.en.html> and is not
activated by default in the browser. The user is responsible for
activating them somehow.
  - The `title` attribute is used to *group* several alternate style
    sheets into a single one. This attribute is otherwise "purely
advisory" as defined in
<http://www.w3.org/TR/html5/document-metadata.html#attr-link-title>.

The current default behavior of the plugin implies having the additional
stylesheet not activated (if you don't set `rel="stylesheet"`) or only
one of them activated (if you add two stylesheets and not set the same
title for both). This was hard to understand for two of us while working
on <https://labs.riseup.net/code/issues/9314> and until we went and read
those W3C documents.

I think that to match better the description of that feature, and to be
easier to comprehend in its default setting, the meta plugin should by
default:

  - Set `rel="stylesheet"`.
  - Not set any `title`.

If we agree on this proposal, I'm willing to provide a patch.

This applies to all versions since c8b4ba3 and until today.
