Added the link of QuickStart at MessagePack official site to README.

Signed-off-by: OZAWA <ozawa.tsuyoshi@lab.ntt.co.jp>
Merge pull request #5 from oza/changed-README

Added the link of QuickStart at MessagePack official site to README.
Update version but hasn't passed test yet.
Disable pgp plugin.
Change Option serialization format.