Many code changes to make everything work with Path and XmlInputFormat. Completes milestone 2.

The existing code works with Files. Hadoop works with [Paths](http://hadoop.apache.org/docs/r2.3.0/api/org/apache/hadoop/fs/Path.html) and [FileSystem](http://hadoop.apache.org/docs/r2.3.0/api/org/apache/hadoop/fs/FileSystem.html) which provide an abstraction over files and file systems. That is to say, Hadoop encapsulates the stuff about distributed or local files and files systems and lets us work with Paths and InputFormats. This pretty much sums up most of the stuff in the commits.

Other than that, I added the XmlInputFormat. I tested with run-extraction-test and everything works. DistRedirectsTest passes. I added some docs too.

Please note that I have taken care to make the commits in a specific sequence. If you make your way from commit 4b9745f to commit d08417f it'll be easier to understand what's going on.

Also, it's worth a mention that you'll need to clone https://github.com/nilesh-c/extraction-framework , switch to the **fromxml** branch and run `mvn install` before building this repo on this branch. I've made a PR to extraction-framework with the changes in **fromxml**.
Yes, that's what I meant. I'll need to write a DistInfoboxExtractor that takes an immutable `seenProperties` as a parameter. I'll probably need to make one MapReduce pass over the dataset to create the `HashSet`, then use it during the main extraction pass (using DistInfoboxExtractor) over the same dataset. That's two passes.

OR, how about this:

I remove the `seenProperties` stuff from DistInfoboxExtractor (or pass it an empty `HashSet[String]`, let the extraction continue. There will be duplicates. Then I simply filter the resulting `RDD[Seq[Quad]]` (parallel collection of results) to remove duplicate `Quad`s in the dataset `DBpediaDatasets.InfoboxPropertyDefinitions`?

Let me know if I'm not expressing this clearly enough, and I'll explain more.