"improvements"

Hi Charles,

I've added some methods from the up-and-coming "spec" (construction with [], to_a, append, add), so I could benchmark Clojr against @Who828 persistent_data_structures as well as hamster. I also had to copy some stuff over from the gem that I didn't find in the repo. gemspec, lib/clojr.rb, Rakefile.

First off doing this kind of JRuby/Java stuff is very new to me (I've done Java a decade ago but am not familiar any more with the tooling). So happy to hear if I'm doing things horribly wrong and learn something.

Second I know this is just an experiment and you weren't sure yet of the approach taken. In the first micro-bench it stack up nicely against Persistent::Vector however so I wouldn't abandon this approach just yet.