Add a test harness

.travis.yml

Cargo.lock

README.md

run-tests.py

samples/build-script/Cargo.toml

samples/build-script/build.rs

samples/build-script/cbindgen.toml

samples/build-script/src/lib.rs

tests/alias.rs

tests/directive.rs

tests/enum.rs

tests/fn-ptr.rs

tests/struct.rs