Add C/C++ FILE* buffer adaptor.

* add function msgpack_fbuffer_write();
* add class msgpack::fbuffer;
* add tests buffer.fbuffer and buffer.fbuffer_c .
Make fbuffer's constructor explicit.
Fix Makefile.am to install fbuffer.h and fbuffer.hpp
Add fclose to fbuffer's tests
Merge branch 'fbuffer'
Add fbuffer.h and fbuffer.hpp to CMakeLists.txt and msgpack_vc.postbuild.bat