feat+fix: deep-level return statements support && half-support for recursion

[pacifiquem]

Now you can return an expression wherever you want in a function!!
This works:

# Writing computer programs in Kinyarwanda

porogaramu_ntoya factorial(a) {
  niba (a == 0 || a == 1) {
    tanga 1
  }
  tanga a * factorial(a - 1)
}

tangaza_amakuru(factorial(5))