Add support for reading ASCII PPM (PBM) format (magic number P1)
Add support for reading ASCII PPM (PGM) format (magic number P2)
Add support for reading ASCII PPM (PPM) format (magic number P3)
Merge pull request #3 from mulander/master

Add support for reading ASCII PPM (PBM, PGM, PPM) format (magic number P1, P2, P3)