Build sources in {GEM_NAME}/tools/{BIN_NAME}/ with the configuration for {GEM_NAME}.
Merge remote-tracking branch 'monaka/pr-build-objs-for-tools-with-conf-for-gem' into develop

Conflicts:
	Rakefile
Use _Bool as mrb_bool if possible.
Use mrb_satic_assert().
Add gem sandbox support.
Define and use Sandbox::Pack
Support "static thread binding".