Consistent style for attribute with given value

[jelovirt]

The 2.0 draft spec uses multiple ways to specify that an attribute has a given value, for example

1. https://github.com/oasis-tcs/dita/blob/DITA-2.0/specification/archSpec/base/processing-keyref-for-links.dita#L11C13-L11C43

   "none" for the <xmlatt>linking</xmlatt> attribute

2. https://github.com/oasis-tcs/dita/blob/DITA-2.0/specification/archSpec/base/example-conref-conaction-replace.dita#L23

    a <xmlatt>conaction</xmlatt> value of <keyword>pushreplace</keyword>

3. https://github.com/oasis-tcs/dita/blob/DITA-2.0/specification/archSpec/base/chunk-attribute-combine.dita#L21

   <codeph>chunk="combine"</codeph>

I know this is due to multiple authors and legacy content, but it would be good if the spec used consistent language to specifying "attribute x with value y" and consistent markup.