Fix .gitignore to not ignore the carp directory under examples
Add a test-case without a `main:` label to trigger a segfault in
carp_vm_make()

This also adds a directory called `fuzz` which isn't very well named,
but maybe one day we can start fuzz-testing Carp. Until then, we can
use this directory to hold use cases that break Carp, and one day a
test-suite that makes sure each commit doesn't break any of them.
Clean up file_read() and avoid a full memset() of contents