Work on multiple pipes support.
Almost have piping working.

Single commands work:
- ls
- cd

Piping is working:
- `ls | grep REA` will return "README.md"

Not working:
- after executing command with pipe, it segfaults with any commands
  afterwards
- the output is buffered to 1024 bytes and read
Fix bug in buildTree that caused piping to not work.
Merge branch 'redirection' of github.com:Glavin001/MRShell into redirection

Conflicts:
	src/execute.c
	src/execute.h