This makes it easier for downstream projects (forks) to replace the
version fetching system with their own. It is as simple as implementing
an interface and overriding the default implementation of
org.bukkit.UnsafeValues#getVersionFetcher()
It also makes it easier for us to organize things like the version
history feature.
Lastly I have updated the paper implementation to check against the site
API rather than against jenkins.
The lock in DataWatcher is used to prevent concurrent modifications
to the 'd' field (entries in MCP). However any modifications to
this map only occur on initialization of an Entity in its
constructor. This modification is write-locked.
Every other access is through a readlock, which allows
the threads to pass if there is no thread holding the
writelock.
Since the writelock is only obtained in the constructor
of the Entity, the further readlocks are actually
useless (which get obtained on set, get, etc calls).
The entries field ('d' currently) has also been declared as
Int2ObjectOpenHashMap to avoid autoboxing on put(), get(), etc
calls.
