Add tests for PangLib.IFF functionality

[pixeldesu]

The libraries functionality needs to be tested.

Note: The focus is not lying on properly parsing game files, as the implementation should be sufficient and any arbitrary structure can be passed to an IFFFile, even completely unrelated to Pangya.

To Do:

• Set up NUnit project PangLib.IFF.Tests
• Create a simple TestStructure used for the tests
• Test writing of files (verify a field using a BinaryReader)
• Test reading of files (using a IFFFile<TestStructure> instance)