chore: make intcode an installable package

- Move intcode/ from 2019/ folder to the root of the repository
- The package is automatically installed with the adventofcode package
  with `pip install -e .` command

adventofcode/2019/day13/day13.py

@@ -8,8 +8,7 @@ from pathlib import Path
 from collections import defaultdict, Counter
 from dataclasses import dataclass
 
-sys.path.append(str(Path(__file__).absolute().parent.parent / "intcode"))
-from intcode import interpret_intcode, Interpreter
+from adventofcode.intcode import interpret_intcode, Interpreter
 
 @dataclass
 class State: