Fix compile error:
  - 'mrb_intern' is renamed to 'mrb_intern_cstr'.
Merge pull request #4 from crimsonwoods/fix_compile_error

Fix compile error:
Trying to solve crash in mob_thread_func

It was tux to a null np->env.
Merge pull request #5 from pbosetti/master

Trying to solve crash in mob_thread_func
Fix build
Add Mutex
Fix Mutex lock/unlock
Add example