Derive Default for schema ast types

[leoyvens]

This makes them easier to construct.

[tailhook]

While it gives the shortest code, is using Default a best way to construct these values? Especially considering that some of them are invalid when constructing default (i.e. empty name).

Maybe it's better to make a fn new(name) method? (except for Schema and Document)

[leoyvens]

For my use case which are unit tests empty names work fine, the default value is not completely unusable.

[tailhook]

It would make more sense if trait would be TestData::generate() instead of Default::default(). Would new("test_data") be too cumbersome for you?

[leoyvens]

That would be fine, I'll update this to add a new(name) instead of Default where that is better.

[leoyvens]

Done, let me know what you think.

[tailhook]

Looks fine. Merged. Thanks!

[tailhook]

Released as v0.2.2