Finally get how to convert strings!!

So it seems that `std.mem.trim` (and likely other functions) don't work
correctly on C strings, or don't work correctly if passed on and coerced
weirdly.

But what helps is converting to a regular zig string/slice using
`std.mem.sliceTo(c_string, 0)`.  It even makes sense, given that `0` is
the nul byte at the end of a c string.  Huh.

Oh, and we run Go thingy now!!

zig/sdl/hello_sdl.zig

@@ -151,19 +151,46 @@ pub fn main() !void {
    }
}
fn runCommand(cmd: []const u8, allocator: *std.mem.Allocator) ?[*:0]u8 {
    const argv = &[_][]const u8{ "/usr/bin/qalc", "-terse", cmd };
fn runCommand(raw_cmd: []const u8, allocator: *std.mem.Allocator) ?[*:0]u8 {
    const cmd = std.mem.trim(u8, std.mem.sliceTo(raw_cmd, 0), &std.ascii.spaces);
    const argv = if (std.mem.startsWith(u8, cmd, "go "))
        &[_][]const u8{ "go", "doc", cmd[3..] }
    else
        &[_][]const u8{ "/usr/bin/qalc", "-terse", cmd };
    for (argv) |arg| {
        std.debug.print("'{s}' ", .{arg});
    }
    const result = std.ChildProcess.exec(.{ .allocator = allocator, .argv = argv }) catch |err| return "oopsie";
    const buf = allocator.allocSentinel(u8, 100, 0) catch |err| return "alloc";
    std.mem.copy(u8, buf, result.stdout);
    std.mem.copy(u8, buf, result.stdout[0..std.math.min(100, result.stdout.len)]);
    var i: usize = result.stdout.len;
    while (i < buf.len) : (i += 1) {
        buf[i] = ' ';
    }
    buf[buf.len - 1] = 0;
    std.debug.print("stderr: '{s}'\n", .{result.stderr});
    defer {
        allocator.free(result.stdout);
        allocator.free(result.stderr);
    }
    return buf;
}
// tests
test "trim []const u8" {
    const untrimmed: []const u8 = "   hey there   ";
    const trimmed = std.mem.trim(u8, untrimmed, &std.ascii.spaces);
    try std.testing.expect(trimmed.len < untrimmed.len);
    try std.testing.expect(trimmed.len == 9);
    try std.testing.expect(std.mem.eql(u8, trimmed, "hey there"));
}
test "trim [*:0]const u8" {
    const untrimmed: [*:0]const u8 = "   hey there   ";
    const to_trim: [*:0]const u8 = " ";
    const trimmed = std.mem.trim(u8, std.mem.sliceTo(untrimmed, 0), std.mem.sliceTo(to_trim, 0));
    try std.testing.expect(std.mem.len(trimmed) < std.mem.len(untrimmed));
    try std.testing.expect(trimmed.len == 9);
    try std.testing.expect(std.mem.eql(u8, trimmed, "hey there"));
}