Skip end of loop in mrb_sym2name_len

Remove RB_GC_GUARD(x) macro.

Cleanup stdio related.

Add accessor: version, description, summary, homepage.

Reduce a snprintf() call in localjump_error().

  C API mrb_p() is always callable.
  - But it will do nothing when ENABLE_STDIO is not defined.

  Kernel#__printstr__ is always callable.
  - But it will do nothing when ENABLE_STDIO is not defined.

Added a link to the contribution guidelines in the README

Move Kernel#sprintf to mrbgem

Replace tabs with spaces

Use MRB_IREP_ARRAY_INIT_SIZE macro. 

Define ARY_MAX_SIZE strictly. Use mrb_int instead of int.

Clean up range.c. Use mrb_int. Use mrb_vtype.

Remove unused var len

mrb_open takes no arguments: (void) instead of ()

cleanup: delete commented out match_op() from parse.y

Adjust some indents

cleanup: unused variable local_svar

Remove trailing whitespaces. This is just a cosmetic change.