RAII based FlatBufferBuilder pool.
Global pool:
```rust use flatbuffers_pool::FlatBufferBuilderPool;
let mut b = FlatBufferBuilderPool::get(); let name = b.create_string("something fun"); b.finish(name, None); ```
Local pool:
```rust use flatbuffers_pool::FlatBufferBuilderPool;
let mut pool = FlatBufferBuilderPool::new().build(); let mut b = pool.get(); let name = b.create_string("something fun"); b.finish(name, None); ```