Added ReedSolomon support

Currently the watermark type byte gets 2 EC codeblocks, the length
designator gets 8 EC codeblocks, and the watermark data of N bytes gets
N EC codeblocks. I'm sure these are not the ideal numbers but the code
runs and seems to have some sort of error correction :)
Added ZXINGNET license and thanks
Fixed unit test to account for ReedSolomon
Update to PNGFile, added test

Added property to PNGFile to reflect storage capacity when SolomonReed
protection is enabled. Added unit test to verify calculation.
Merge pull request #2 from tslater2006/reed-solomon

Reed solomon