pgm 22.7, free output filename on file open error
pgm 22.7, rle: dynamically allocate and grow output buffer
pgm 22.7, rle: extract encoding algorithm into passable function so file IO won't have to be duplicated for decode
pgm 22.7, rle: roughly working decode algorithm, with bugs yet
pgm 22.7: files that rle encodes incorrectly but consistently