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.

Also, it would be useful to have a travis link in readme.md.

Commit 42343eb contains a more controversial change to the makefile. I've completely removed the version-script command. It needs to be readded on ELF platforms. I don't know the correct way of detecting platforms in a make file in order to perform this though.