12 test cases for two or more pipes
Merge branches 'master' and 'master' of https://github.com/azatris/cs4218

# By Mingxia Liu
# Via Mingxia Liu
* 'master' of https://github.com/azatris/cs4218:
  Modified to delete all temporarily created files

# By Mingxia Liu
# Via Mingxia Liu
* 'master' of https://github.com/azatris/cs4218:
  Modified to delete all temporarily created files