Add docs about build, tests, and generating docs to README

Signed-off-by: Tsuyoshi Ozawa <ozawa.tsuyoshi@gmail.com>
Add how to build msgpack-ruby.
Add how to build with respect to 'Bundler'.
Getting msgpack to work with Ruby v2.0
Merge pull request #10 from oza/build-docs

Add docs about build, tests, and generating docs to README
Merge pull request #15 from suzukaze/add-how-to-build

Add how to build msgpack-ruby.
Merge pull request #16 from thegreendroid/master

Getting msgpack to work with Ruby v2.0
Add write_ext_header
Add write_ext_value
Add unpacking of Extensions
Move `fixext n` condition outside case statement
Add C MessagePack::Extended class

* Remove Ruby MessagePack::Extended class
* Move delegete_to_pack and ENSURE_PACKER to packer_class.h
* Make msgpack_packer_write_ext_value access the instance methods `type` and
  `data` instead of just instance variables.
Extract read_extended_body_begin
Fix: packing ext type is returning 0
Check for type range error during init
Add spec checking for packed result
Add parenthesis to remove ambiguity
Rename Extended_to_eql to Extended_eql
Check for sameness of class for Extended.eql?