2018_01.py: Rename solve() to solve_part_one()
2018_01.py: Rename solve() to solve_part_one()

robjwells/adventofcode-solutions,robjwells/adventofcode-solutions,robjwells/adventofcode-solutions,robjwells/adventofcode-solutions,robjwells/adventofcode-solutions,robjwells/adventofcode-solutions