add automatic json conversion for attributes

[hhaensel]

This PR addresses #231.

It requires adaptation of the respective functions in StippleUI to allow for Vectors or Dicts.

E.g. with

function btntoggle(fieldname::Symbol,
                args...;
                options::Union{Symbol, Vector{<:AbstractDict}},
                kwargs...)

  q__btn__toggle(args...; kw(
    [Symbol(":options") => options, :fieldname => fieldname, kwargs...])...)
end

we could write

julia> import Stipple.opts

julia> btntoggle(:network, options = [opts(label = x, value = lowercase(x)) for x in ("Google", "Facebook")])
"<q-btn-toggle v-model=\"network\" :options=\"[{'value':'google','label':'Google'},{'value':'facebook','label':'Facebook'}]\"></q-btn-toggle>"

julia> select(:selector, options = ["a", "b", "c"],)
"<q-select v-model=\"selector\" :options=\"['a','b','c']\"></q-select>"

[essenciary]

@hhaensel is this breaking or the current syntax is still supported?

[essenciary]

@hhaensel nothing to comment regarding the code and I can't see anything off. Does it require more testing? If tests pass, it's good to go IMO.

[hhaensel]

@hhaensel is this breaking or the current syntax is still supported?

Old syntax is, of course, still supported. Some adaptiations will needed to be made in StippleUI to support the new attribute handling.
That's already waiting 😉