Changes

`AreaContainmentObject` and `BiomeTag` examples (#2394)

* Add `AreaContainmentObject` tag examples.

Also de-dented code for 'spawnable_blocks' to make it look more uniform :)

* Add `BiomeTag` tag examples.

Mechanism not done as they can't be tested currently.
Fixed up some funky new lines here and there.

* Add better example for `<BiomeTag.downfal_type>`

* Change `<BiomeTag.downfall_type>` one more time.

Returns specific data, and so it should probably be shown in the example.

* Update a few examples to have more clear comments.

* Clean up and `BiomeTag` mech examples.
 (commit: 475612b)