Attr values can now be given as normal Lua tables; this can be used as a
convenient alternative to define Attr values, instead of constructing
values with `pandoc.Attr`. Identifiers are taken from the *id* field,
classes must be given as space separated words in the *class* field. All
remaining fields are included as misc attributes.
With this change, the following lines now create equal elements:
pandoc.Span('test', {id = 'test', class = 'a b', check = 1})
pandoc.Span('test', pandoc.Attr('test', {'a','b'}, {check = 1}))
This also works when using the *attr* setter:
local span = pandoc.Span 'text'
span.attr = {id = 'test', class = 'a b', check = 1}
Furthermore, the *attributes* field of AST elements can now be a plain
key-value table even when using the `attributes` accessor:
local span = pandoc.Span 'test'
span.attributes = {check = 1} -- works as expected now
Closes: #5744