v2.0.0

Version 2.0.0 brings better concurrency, atomic transactions with arbitrary
operations, zero cost read-only snapshots, database backup, and more, all with a
simpler and more scalable internal architecture.

Refer to the upgrade guide for how to
upgrade from previous versions.

• [breaking] The functions CubDB.get_and_update/3,
  CubDB.get_and_update_multi/3, and CubDB.select/2 now return directly
  result, instead of a {:ok, result} tuple.
• [breaking] CubDB.get_and_update_multi/4 does not take an option argument
  anymore, making it CubDB.get_and_update_multi/3. The only available option
  used to be :timeout, which is not supported anymore.
• [breaking] Remove the :timeout option on CubDB.select/2. This is part of
  a refactoring and improvement that moves read operations from an internally
  spawned Task to the client process. This makes the :timeout option
  unnecessary: by stopping the process calling CubDB, any running read
  operation by that process is stopped.
• [breaking] CubDB.select/2 now returns a lazy stream that can be used with
  functions in Enum and Stream. This makes the :pipe and :reduce
  options unnecessary, so those options were removed.
• Add CubDB.snapshot/2, CubDB.with_snapshot/2 and
  CubDB.release_snapshot/1 to get zero cost read-only snapshots of the
  database. The functions in CubDB.Snapshot allow to read from a snapshot.
• Add CubDB.transaction/2 to perform multiple write (and read) operations in
  a single atomic transaction. The functions in CubDB.Tx allow to read and
  write inside a transaction.
• Add CubDB.back_up/2 to produce a database backup. The backup process does
  not block readers or writers, and is isolated from concurrent writes.
• Add CubDB.halt_compaction/1 to stop any running compaction operation
• Add CubDB.compacting?/1 to check if a compaction is currently running
• Move read and write operations to the caller process as opposed to the
  CubDB server process.
• Improve concurrency of read operations while writing