Support hessian 2.0 decode. #8

* Add Date hessian 2.0 decode.
* add double, int hessian 2.0 support
* decode compact long, but four octet longs not impl
* support decode hessian string 2.0
* add java HashMap decode
* Read hessian 2.0 Object and Class
* support hessian 2.0 ref
* support hessian 2.0 readType
* support read hessian 2.0 List
* update byte to 0.2.1, use getInt8()
* update hessian 2.0 readme
Support hessian 2.0 encoder.

* int encode hessian 2.0
* encode hessian 2.0 long
* Support encode hessian 2.0: double, date, bytes and string
add hessian 2.0 decoder