Add meta element to info

Here is the first issue from Norm's list.  He has proposed:
PR 155, Add a general 'meta' element in info.
The element
would be <meta name= foo  content= bar />, and would provide
a mechanism for adding miscellaneous metadata in the content
attribute, with a name attribute to specify its purpose.  This PR
implements the change suggested in Issue #153.
https://github.com/docbook/docbook/pull/155
I'm in favor of this change.  It adds a lightweight (empty)
element to support capturing small bits of metadata that don't fit
any of the other info categories. It's limited because the data
has to fit in an attribute value, but I think that's ok.  I've
frequently needed something like this.
Discussion?

--
Bob Stayton