macro add_init(type::Expr)

Automatically add a constructor for building objects with dict and json to DataType

Examples:

    @add_init struct Test
        field:AbstractString
    end

    Test("{"field":"a"}") == Test("a")
    Test(Dict("field"=>"a")) == Test("a")

macro add_init(symbol::Symbol)

Automatically add a construction method for building objects with dict and json 
to the DataType, and adapt to the DataType modified by base.@kwdef

Examples:

    @Base.kwdef struct Test
        a::Int
        b::Int=2
        c::Int
    end
    @add_init Test

    Test(Dict("a"=>1, "c"=>3)) == Test(1,2,3)