puts
As CRuby behaves.
Kernel#print
Kernel#puts
mruby-print
mruby-sprintf
In the old implementation, `Kernel#printf` raise error if `mruby-sprintf` gem isn't specified before `mruby-print` gem. The new implementation eliminates this ordering issue. This way is the same as `Kernel#printf` and `IO#printf` in `mruby-io` gem.
Kernel#sprintf
Kernel#p
Although the return value is not defined in ISO, it is better to behave as CRuby does.