Fix arena size check.
Adjust space
Merge pull request #917 from matsumoto-r/adjust_space

Adjust space
Merge pull request #913 from carsonmcdonald/arena_check_fix

Fix arena size check.
Remove unused structures.
Move the place of a curly bracket. This is just a cosmetic change.
Pluggable Struct
Add typedef to structures that have mrb_ prefix. Use typedef-ed type instead of struct directly.
Pluggable Struct
Merge branch 'master' into pluggable_struct
Gemify
Move mrblib for Struct
format some source code (class.c)
Merge pull request #919 from monaka/pr-use-typedef-names-as-possible

Use typedef names as possible
Merge pull request #921 from skandhas/pr-format-class-source

format some source code (class.c)
Merge pull request #918 from monaka/pr-remove-unused-struct-and-more

Remove unused struct and more
format some source code (vm.c)
Should be MRB_DATA class. RStruct isn't managed by mruby core. So it should be self-managed class instances.
Fixed GC guard
Fix copy values