Allow clj-v8 to be bundled in an uberjar

- clj-v8 fails in an uberjar, since it relies on its files to be
  accessible on the file system.

- this is because JNI and JNA relies on the native binaries to be on the
  file system.

- so in order to be bundled in an uberjar, we have to copy the files out
  to a temporary location when loading the native library.

The entire investigation can be read for your amusement or horror in https://github.com/circleci/stefon/issues/9.

I have not been able to run your tests - since that too results in a UnsatisfiedLinkError (see #6), but I have packaged this version in our uberjar, and that works.