Added `repl:assembly` and `repl:dist` tasks to the build.

You should be able to just run the following and drop straight into a repl with the current scoobi source:
```
./sbt "repl:dist" 
HADOOP_CONF_DIR=somewhere ./target/scoobi-repl-0.8.0-SNAPSHOT/scoobi
```

Basically the changes are:
 - `repl:assembly` builds a fat jar as per what the old repl sub project did.
 - `repl:dist` builds a directory, `target/scoobi-repl-${version}`, containing a runnable repl and tar balls up the directory at `target/scoobi-repl-${version}`
 - this change removes the repl sub project
 - I took some liberties with the shell script so just check what I did. Basically changes so it would work on bsd, osx and linux, and drop the version number from the jar it references (the `repl:dist` task creates a symlink for the general name from the versioned name)
 - The code around creating the distribution is pretty funky and may require a revisit, yell if you want me to do it now.