Working Shell without errors or leaks

This release incorporates all of the major functions of a working shell. Without any errors or memory leaks.

Features:
Custom builtins:

• help
• cd
• setenv
• unsetenv
• env
• alias
• unalias
• history
• arsine

Checks PATH for executable files like /bin/ls if no directory is given
Builds a custom abstract syntax tree to take in and execute more complex commands with pipes, redirection, etc

initial beta release for Holberton School review

This release incorporates all of the major functions of a working shell.

Features:
Custom builtins:
- help
- cd
- setenv
- unsetenv
- env
- alias
- unalias
- history
- arsine
Checks PATH for executable files like /bin/ls if no directory is given
Builds a custom abstract syntax tree to take in and execute more complex commands with pipes, redirection, etc