Solving Advent of Code using Zig

Edited build.zig to accept year, day, and part args:

zig build -Dyear=2023 -Dday=1 -Dpart=1

Note: year and day args are optional, they will default to todays year and day, part is mandatory (subject to change) and is either 1 or 2, e.g:

zig build -Dpart=2

• Generate directories and files using a template