Include stddef.h. It is required by size_t. In case you include stdio.h, stddef.h is included indirectly.
Separate FILE dependencies with ENABLE_STDIO.
Reduce using snprintf(). They can replace by mruby API.
Add stdio.h. This is just for now. We should discuss about remote tests later.
Merge pull request #1065 from monaka/pr-reduce-stdio-dependency

Reduce stdio dependency