`amount` and `halve` implementation for `Dict` and `DictView` is wrong

[MasonProtter]

This seems to assume some maybe bad things about Dict.

e.g.

julia> using SplittablesBase: amount, halve

julia> d = Dict(:a =>"one", :b=>"two", :c=>"three", :d=>"four", :e=>"five");

julia> l, r = halve(d);

julia> amount(d), length(d)
(16, 5)

julia> amount(l), length(l)
(8, 4)

julia> amount(r), length(r)
(8, 1)

[longemen3000]

i think you can get a better estimate by just using d.count ÷ 2 instead of doing what is being done right now (but it would be still different to length)