Updated the function symtbl_hash as per instructions

No testing has been done yet, but the function should be implemented as per the
instructions provided in class and the in-code documentation.
Updated the function symtbl_lookup as per instructions

No testing has been done yet, but the function should be implemented as per the
instructions provided in class and the in-code documentation.
Updated the function symtbl_dump_entry as per instructions

No testing has been done yet, but the function should be implemented as per the
instructions provided in class and the in-code documentation.
Updated the function symtbl_dump_current as per instructions

No testing has been done yet, but the function should be implemented as per the
instructions provided in class and the in-code documentation.
Updated the function symtbl_dump_all as per instructions

No testing has been done yet, but the function should be implemented as per the
instructions provided in class and the in-code documentation.
Updated the function symtbl_exit_one_level as per instructions

No testing has been done yet, but the function should be implemented as per the
instructions provided in class and the in-code documentation.