[Bleeding] Update Javadoc for setMaxSpeed(). Addresses BUKKIT-4242

The default maxSpeed has changed in vanilla from 0.4 to 0.35 - this commit
updates the Javadocs to reflect that fact.
[Bleeding] Implement get/set damage method for boats. Adds BUKKIT-5325

This brings the same functionality to boats that currently exists only for
minecarts.
[Bleeding] Deprecate occupiedDeceleration

Due to changes in how Minecraft handles boats, this value is no longer
constant, but instead dynamically calculated based on other variables.