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/day7/day7.py

@@ -1,10 +1,7 @@
 import sys
 from pathlib import Path
-
-sys.path.append(str(Path(__file__).absolute().parent.parent / "intcode"))
-
 from itertools import cycle, permutations
-from intcode import interpret_intcode, Interpreter
+from adventofcode.intcode import interpret_intcode, Interpreter
 
 def main(inp):
     mem = list(map(int, inp.readline().rstrip().split(",")))