Merge pull request msgpack#823 from redboltz/update_to_3.2.1

Updated the version to 3.2.1.

Merge pull request msgpack#823 from redboltz/update_to_3.2.1

Updated the version to 3.2.1.

Merge pull request msgpack#785 from redboltz/update_version_3.2.0

Updated the version to 3.2.0.

Merge pull request msgpack#727 from redboltz/update_311

Updated the version to 3.1.1.

Merge pull request msgpack#723 from redboltz/update_readme

Updated readme.

Merge pull request msgpack#686 from redboltz/fix_685

Fixed msgpack#685.

Merge pull request msgpack#681 from redboltz/update_doc_to_v3.0.0

Update the document for the version 3.0.0.

Merge pull request msgpack#625 from redboltz/update_to_215

Updated the version to 2.1.5.

Merge pull request msgpack#621 from redboltz/v2.1.4

Updated the version to 2.1.4.

Updated README.