Add code reading memo
Format code reading memo
Refine env structure
Add descriptions about `root' and change format to markdown
Commit temporarily
Rewrite gc() with simple mark&sweep GC
Merge remote-tracking branch 'origin/mark_and_sweep-1' into develop
Expand heap size to 8KB from 4KB
Merge remote-tracking branch 'origin/mark_and_sweep-1' into develop
Add missing mark cleaning and refactor mark phase
Merge remote-tracking branch 'origin/mark_and_sweep-1' into develop