Feature stage 9

See merge request jjb18163/cs210-shell!2

Feature stage 8

See merge request jjb18163/cs210-shell!1

- Create save_aliases function

- Modify load_aliases function

- Modify set_alias to use add_alias

- Replace functions get_alias_value with get_alias_index

- Remove .vscode folder

- Added history functionality from stages 5 and 6

- Fixed an out of array bounds bug in unalias function

- Added documentation in header file

- Fixed bug in load_history function

- History array is freed in save_history function

- Added functionality from previous stages

- Added documentation in header file

- Added more detailed error messages

- Added functionality from pervious stages

- Separated code into smaller functions

- Added documentation in header file

Changed alias functionality; made separate functions for commands; solved memory leak issues in tokenize, alias and unalias