use mrb_intern_lit in mruby-random
add 'd' format specifier to get data pointer directly from mrb_get_args
use 'd' format spec to get Random object
Merge pull request #1721 from take-cheeze/d_format_spec

add 'd' format specifier in mrb_get_args and mruby-random gem improvement
avoid accessing uninitialized string; ref ac936fc