Correct compiler warnings / errors on Mac Clang 5.1

Fix type issues (uint64_t -> size_t). ookread expects a size_t for the bricksize parameter instead of a uint64_t. Also fixes a printf() warning regarding off_t. I have been unable to test the printf code because I have a linker error that needs resolution and I will submit a separate pull request for.

Also, it would be useful to have a travis link in readme.md.