Return values + Makefile + .gitignore

```
tomaskorcak@kx-mac c4 (master) $ make test
./c4 hello.c
hello, world
exit(0) cycle = 9
./c4 -s hello.c
1: #include <stdio.h>
2:
3: int main()
4: {
5:   printf("hello, world\n");
    ENT  0
    IMM  864256
    PSH
    PRTF
    ADJ  1
6:   return 0;
    IMM  0
    LEV
7: }
    LEV
tomaskorcak@kx-mac c4 (master) $
```
@rswier could you merge this or #1 to get the return types correct for the methods?

Seems all pull requests out there are requesting this change.