Custom associative type to use when parsing TOML objects

[gryumov]

using TOML, OrderedCollections

TOML.parse(toml, dicttype = OrderedDict{String,Any})

[OmegaLambda1998]

Could you do this by changing:

mutable struct Parser
    ...
    root::AbstractDict
    ...
end

So that you could do, for instance:

parser = TOML.Parser()
parser.root = OrderedDict{String, Any}()
TOML.parse(parser, toml)

[OmegaLambda1998]

It's a bit more complicated then I suspected, but I think I got it working in the above pull request