Add mrb_expr.c as place holder
Add scan_info API - grn_scan_info_put_logical_op() and grn_scan_info_get_arg()
Copy scan_info_build() to lib/mrb/mrb_expr.c
Remove unnecessary/unimplemented functions
build scan_info through ruby method
Merge pull request #110 from wanabe/scaninfo-with-mruby

Building scan_info by mruby method

Patch by wanabe. Thanks!!!