Finish all Integer ISO Tests

don't close stdin.

Minor edits to test suite and Math module

Added some tests for Math module. Some refactoring in math.c; numeric tolerance exported as Math::TOLERANCE and also used for fuzzy tests in mrbtest suite

remove mrb_parse_nstring_ext; use mrb_parser_new() then set p->capture_error = 1; then call mrb_parser_parse(); see tool/mirb/mirb.c