Deprecating the Mallard mime attribute

[Shaun McCance <shaunm gnome org>]

For those of you not on mallard-list, I wanted to let you know about a
deprecation in the upcoming Mallard 1.1. In Mallard 1.0, you mark the
content type of a code block with the mime attribute.

<code mime="text/x-csrc">

In Mallard 1.1, the mime attribute will be deprecated in favor of the
simpler type attribute, which takes a short string.

<code type="c">

You can even use a space-separated value.

<code type="xml mallard">

I could use help with testing and updating the documentation. Here are
some links for more information:

https://blogs.gnome.org/shaunm/2019/01/07/easier-syntax-highlighting-wi
th-mallard/
http://projectmallard.org/pipermail/mallard-list/2019-January/000273.ht
ml
http://projectmallard.org/mep/mep0010

Thanks,
Shaun