Multiline array option for dumps

[dbohdan]

It would be useful for my project Remarshal and likely for other downstream users of TOML Kit to be able to tell toml.dumps to output multiline arrays. For example, you could call toml.dumps(foo, multiline=True) for only multiline arrays, call toml.dumps(foo, multiline=5) and make arrays with five or more items multiline, or have it based on the line length. Without this feature, you either get output like my TOML example or have to construct the document manually.

The option could also apply to inline tables if a future TOML spec added them.