[B+C] Add fire example to BlockFadeEvent javadoc- Fixes Bukkit-4835

#### Description:  
##### The Issue:
BlockFadeEvent is already called for flammable blocks fading out, but not for inflammable.

##### Justification for this PR:
Inform developers that BlockFadeEvent is being used for fire out.

##### PR Breakdown:
Also modified javaDocs for BlockFadeEvent to add fire example.
 
##### Testing Results and Materials:
not needed

##### Relevant PR(s):  
C-1253-https://github.com/Bukkit/CraftBukkit/pull/1253 - add BlockFadeEvent call
 
##### JIRA Ticket: 
BUKKIT-4835 - https://bukkit.atlassian.net/browse/BUKKIT-4835