Testing: Moving over to Test::More

Test::Simple is really a very simple module. Its sole exported function is the "ok" function.

Test::More has the same "ok" function - so it is a drop-in replacement - but it also has lots of other functions and tools:

```
ok
```
```
is
```
```
isnt
```
```
diag
```
```
like
```
```
cmp_ok
```
```
is_deeply
```
```
SKIP
```
```
TODO
```
```
done_testing
```
```
subtest
```

Better error reporting.

In the end every test can be based on the single ok() function. The additional functions mainly serve as convenience methods to allow better error reporting.