Returns BaseRecords instead of MemoryRecords

We can write a record which is a subtype of BaseRecords, but we can not read a record which is a subtype of BaseRecords. If we change the return type of Readable#readRecords from MemoryRecords to BaseRecords, we can override the implementation of readRecords and returns a subtype of BaseRecords easily.

We known that the MemoryRecords is based on JDK's ByteBuffer. We are developing a netty project(kroxylicious) and we want to create a subtype of BaseRecords like MemoryRecords based on netty's ByteBuf.