Initial code to start dispatching coprocessor events.

This code doesn't work yet.
Exclude HBase's old JRuby.
Add JCL dependency.

JCL is a library which will let us properly load a modern JRuby from
within an HBase coprocessor.
Rename `.jars` to `jars`.
Add runtime dependencies to gem output.
Add `jars` to require_paths.
Load runtime dependencies from gem directly.
Move classpath helpers into `askari` and publish `runtime_classpath`.
Actually, let's just unpack our dependent JARs since it means we don't
have to use two custom classloaders.
Actually, just dump everything into the `classes` directory.

This keeps the Askari::Packaging module simple.
Use ChildFirstClassLoader from http://articles.qos.ch/classloader.html.

JCL does not properly implement the ClassLoader.getResource function,
and thus does not work for embedding JRuby. I've submitted a pull
request for partially implementing this support, but I don't know if
it will be accepted upstream.

https://github.com/kamranzafar/JCL/pull/10

If JCL does eventually accept that pull request we can switch back to
using it instead of this bare bones class loader.
Fix class loading issue due to URLClassLoader's parent-first policy.
Drop JCL dependency for now.
Remove `mrproper` task.

It's just a bad idea.