Fix #107

[Rog3rSm1th]

This PR Fixes #107.

For example this program:

%builtins output

func sum2(x: felt, y: felt) -> felt {
    return x + y;
}

func main{output_ptr: felt*}() {
    let x = 1;
    let y = 2;
    let sum = sum2(x, y); 
    return ();
}

You can determine the values of x and y needed for the sum to be 10 with this command:

thoth local tests/json_files/cairo_0/cairo_felt_sum.json --symbolic -function __main__.sum2 -constraint v4==10 -solve v0_x v1_y

v0_x: 10
v1_y: 0