Unsupported YAML features used by other map editors

[PhoenixBound]

(Originally posted as pk-hack/CoilSnake#306)

The version of SnakeYAML in the version of EB Project Editor bundled with CoilSnake 4.2 does not follow certain YAML features like references in the same way as PyYAML 6.0.2 (used by EBME). When these features are used, EB Project Editor seems to throw up its hands and end up with a null, which is then saved into the file.

Test new builds of EBProjEditor (with new versions of SnakeYAML) to see if they also suffer from this issue, and whether there are any workarounds if so.

[Supremekirb]

For the record, references shouldn't be used in EBME since cfa0a9d, which was included in release 0.2.0. Are there any other modern YML features that EBME is using that I'm unaware of?