Add complex TOML test data

[mondeja]

The unique problem that I see in the implementation is that JSON does not accept date types, so these must be defined as strings and checked using format. The solution that I see is to convert Python date objects into strings after parsing. Unfortunately, tomli does not offer an argument to convert date values as it does for floats.

I would appreciate some guidance for this task if you don't want to work on it.

Contributes to #95

[sirosen]

@mondeja, thanks so much, this is awesome! It's more complete and more thorough than I was hoping.

I'd like to keep the "simple case" data, and I'll add handling to convert datetimes back into their string representations. So I'll make a commit on your PR branch which makes those changes -- plus gives you a shout-out in the changelog -- and assuming it passes CI I'll merge.

[sirosen]

I've just merged this along with some work to support TOML's first-class date and time types. It may be a few days before this is released, however. These changes revealed a bit of an issue with the way that format checkers were being built, and I need to think a little about whether or not I need to make additional changes.