(doc) an improvement of Japanese in CONTRIBUTING.md

Improved Japanese in CONTRIBUTING.md
Merge pull request #58 from Nyoho/doc-improve-japanese

(doc) an improvement of Japanese in CONTRIBUTING.md
Fix issue in Windows where PMXViewer runs faster than 60fps
Added some small troubleshooting notes to English readme
Simplified and changed initialization of rigid bodies using D3D<->OpenGL conversion func.
Fixed shape size of rigid bodies
Refactored and added rotation flipping of PMX
Cosmetic change of print debug code
Omit unnecessary bone transformation update

PMXBone::Local is now initialized in readPMX().
Then there is no need to update bone transformation matrices
which do not have motion.
Fixed #45 movement of type 2 rigid bodies is incorrect

Now hair of Apearance Miku and TDA Miku looks OK.
Changed symbolic macro to enum

This improves doxygen-generated documentation and helps
debuggers and compilers to use additionaldebug informations
and type checking.
Tweak gravity for realistic physics
Merge branch 'type2_rigid_bodies' of https://github.com/yocchi/MikuMikuPenguin into yocchi-type2_rigid_bodies
Remove unused icon from repository