API improvements

Improvements found while using the portals API in another mod (cloudlands):
* remote_portal_checkup() will check the whole portal and frame for mapgen overwrites.
* Allow find_realm_anchorPos() to return nil if no realm location could be found (portal will fail to ignite).
* Allow create_book_of_portals() to be invoked [indirectly] by other mods.

Also lowers nether_book_close.png to be 4bpp
This commit is contained in:
Treer
2020-02-08 18:00:01 +11:00
committed by SmallJoker
parent 32e5d818e8
commit 7939161535
6 changed files with 39 additions and 29 deletions

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