Syscalls, STD library & Conditional Compilation

[H1ghBre4k3r]

This PR aims to provide an abstraction over common syscalls to reduce the number of builtin functions.

These abstractions are encapsulated within a new std.why module.

Furthermore, this PR introduces conditional compilation via compiler directives (currently, this only works for depending on different operating systems):

#[os == "linux"]
let value := "We are on linux"

#[os == "macos"]
let value := "We are on macOS"

This feature is currently used to distinguish different syscalls on macOS and Linux.

Closes #29