Add property based testing with quickcheck

[fitzgen]

https://github.com/BurntSushi/quickcheck

Another kind of fuzzing of sorts. We should use quickcheck to generate struct definitions and whitelisting/opaque/etc rules, generate a header containing those definitions in C source form, run bindgen on the header, and then assert various properties about the resulting bindings.

Ideas of properties to assert:

• bindgen doesn't panic
• the resulting bindings compile
• the resulting bindings layout tests pass
• whitelisted types appear in the bindings

All of these rely on generating valid C headers, not just garbage, which is a little bit of work, but seems do-able.

[shnewto]

@fitzgen Any opinion on the status of this issue? "property based testing with quickcheck" exists now but there's still room for expanding the scope. Maybe tests for whitelisting and opaque types should be added before closing? Maybe some generated C++?

[fitzgen]

I think we can close this issue now -- thanks for all your work thus far!