Add test cases for FlateDecode post-decode prediction

[gunnsth]

Should test:

1. TIFF encoding prediction
2. PNG prediction

• None, Sub, Up, Average, Paeth, Combination

Include cases with 1,3,4 color components.

Can assume BitsPerComponent = 8 for now. Support for more BPC will be included in a separate ticket which will include making tests.

[gunnsth]

Tests for PNG prediction part of #320 Would be good to test cases with overflow too Still need tests for TIFF prediction