[B+C] Added cauldron events. Adds BUKKIT-5597 and BUKKIT-5598.

##### The Issue:
In present state, you can't detect when cauldron fills with water due to rain (BUKKIT-5597) or when living entity extinguish itself by going inside cauldron with water (BUKKIT-5598).

##### Justification:
With that change you can use BlockFormEvent to detect when cauldron fills with water due to rain and use BlockFadeEvent to detect when living entity extinguish itself by going inside cauldron with water.

##### PR Breakdown:
This PR updates documentation to address additional uses for BlockFormEvent and BlockFadeEvent.

##### Bukkit PR:
[Bukkit/CraftBukkit#0000](https://github.com/Bukkit/CraftBukkit/pull/0000)

##### JIRA Ticket: 
[JIRA Ticket #5597](https://bukkit.atlassian.net/browse/BUKKIT-5597)
[JIRA Ticket #5598](https://bukkit.atlassian.net/browse/BUKKIT-5598)