#3 BURG spec doc needs to be updated

[Tom Harwood]

JBurg's spec says it support ReturnType void -- the
grammar chokes on this usage.

[Tom Harwood]

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Probably going to "fix it in doc" -- the emitters are
written with the idea that something will be returned from
the reductions.

[Tom Harwood]

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The specification says nothing about ReturnType void, but it
does need considerable updating, e.g., it doesn't know about
per-state ReturnType directives.

[Tom Harwood]

Re-purposed this defect to note that the specification doc in general needs an update.