Add comments.
Allow programmers to specify build path manually
Repalace int with mrb_bool because a return value is boolean.
Merge pull request #1385 from suzukaze/refactor-return

Repalace int with mrb_bool because a return value is boolean.
Fix warning by making call explicit
Merge pull request #1384 from xxuejie/customize-build-dir

Allow programmers to specify build path manually
Merge pull request #1388 from carsonmcdonald/toplevelwarnfix

Fix warning by making call explicit
Fix string test for so that it works for int16
Save mirb history when readline enabled
Use env[USERPROFILE] for Windows
Changed use of MRB_INT_MAX to MRB_INT_MAX-1
Merge pull request #1391 from carsonmcdonald/fixfallbackarraysize

Changed use of MRB_INT_MAX to MRB_INT_MAX-1
Merge pull request #1389 from carsonmcdonald/stringtestfix

Fix string test for so that it works for int16
Merge pull request #1390 from kyab/mirb_history

Save mirb history when readline enabled
Merge pull request #1382 from suzukaze/add-comments

Add comments in irep.h