This proves to be more reliable than Agreno's UnsafeBuffers.

This matches the existing LICENSE.TXT spelling and the spelling of the
license we are using: https://httpd.apache.org/docs/trunk/license.html

JNR-FFI's TransientNativeMemory was prematurely deallocating off-heap
memory before LMDB syscalls completed. Return transient pointers from
BufferProxy.in() and use reachability fencing at all call sites to
prevent premature GC.

BufferProxy and KeyVal were also simplified to remove pointer address
passing, given this is inexpensively available from the
Pointer.address() accessor (which is backed by a final field).

This is an API breaking change if external users implemented their own
BufferProxy, however it is considered unlikely many (if any) users
would have ever done this.

Fixes lmdbjava#252

…ignored

Fix resulting buffer from BufferProxy's out method being ignored.

…y-bug