Psr0Fixer to tokens

I've rewritten the Psr0Fixer to use tokens instead of raw string, and I've added a leading `<?php` to all test-cases to make `token_get_all` work.

There's one test that fails though: the leading namespace test. Is it truly required behaviour for the fixer to remove leading whitespace? (it isn't mentioned in the PSR-0 standard)

This PR implements the last TODO in #489.
Actually, there are test-cases like that:
```php
<?php namespace Test;
```
gives the following tokens:
```php
php > var_dump(token_get_all('<?php namespace Test;'));
array(5) {
  [0] =>
  array(3) {
    [0] =>
    int(374)
    [1] =>
    string(6) "<?php "
    [2] =>
    int(1)
  }
  [1] =>
  array(3) {
    [0] =>
    int(383)
    [1] =>
    string(9) "namespace"
    [2] =>
    int(1)
  }
  [2] =>
  array(3) {
    [0] =>
    int(377)
    [1] =>
    string(1) " "
    [2] =>
    int(1)
  }
  [3] =>
  array(3) {
    [0] =>
    int(308)
    [1] =>
    string(4) "Test"
    [2] =>
    int(1)
  }
  [4] =>
  string(1) ";"
}
```

I could check whether the previous token ends with space if `$token->isWhitespace() === false`, and add a newline if the token doesn't end with a spacey character.