Less 'extern "C"' also reorganized mruby.h
moved definitions of mrb_code and mrb_aspec to mruby/value.h
Integrated vm into RBasic now every mruby object knows it's vm ( should
help with vm1-vm2 object passing)
Preparing to apply the mruby fiber support.
Brought the fiber implementation with mruby master.
mruby/mruby@2b1ca488fb50d9db526c1b887b39bd6db113d4f8