- Updated implementations to return a ReadOnlyList around an array (to reduce wasted memory from exposing lists or lazy enumerators around lists).
- Protect non-public ISpriteFrame classes by making them inner classes to prevent casting.
- Added an AsReadOnly extension method for lists.
There is a strange issue that appears* when Theater calls
ISpriteFrame.Frames on the R8Reader. The R8Reader uses
IEnumerable.Cast<> which behaves slower and slower, which
makes map loading become 10+ times slower.
The changes here simply avoid the casting.
[*] This happens at least on Linux x86_64 with Mono 3.2.8.
See https://bugzilla.xamarin.com/show_bug.cgi?id=19668
