Fix Hadoop 2.2.0 support, upgrade to Spark 0.8.1

This is a continuation of @arahuja's PR #39 with the following changes:

1. Fixed the "No Filesystem found for scheme: ..." errors by merging the `META-INF/services` files when building the shaded assembly JAR.
2. Modifies the POM so that the default `hadoop.version` setting of 2.2.0 produces a working build without having to additionally enable a Maven profile.