Ignore case when looking for iTunes extension namespace

[andy128k]

Closes #158

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (2accbd7) 81.46% compared to head (1ea0254) 81.61%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #159 +/- ## ========================================== + Coverage 81.46% 81.61% +0.14% ========================================== Files 23 23 Lines 1538 1545 +7 ========================================== + Hits 1253 1261 +8 + Misses 285 284 -1 ```

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