Release 2.0.0 beta 3

Changes from 2.0.0-beta.2 to 2.0.0-beta.3

• Quick release to fix that beta.2 was tagged on top of a branch, not master.

• The msgpack trailer now properly starts with 0x90 + 4 value, not plain
  wrong 0x09 + 4.

• Trailer version bumped to 1.