Nutch structure build. The behavior is the same of DgIndexer for now.

This commit is part of issue #23

Fix the README.md of dgIndexer package.
issue #23 incomplete. 

New Structure created (InvertedIndex). The Reducer must build all the index previously to emmit the final output.

Add a helper class, CastingTypes, for simplify the casting types among Hadoop and Java datatypes.
Advances on issue #23.

The Indexer isn't work properly. The generated index see like that:

```
1	org.apache.hadoop.io.MapWritable@fa2ff3bc
2	org.apache.hadoop.io.MapWritable@faa9c246
3	org.apache.hadoop.io.MapWritable@b57dab4
4	org.apache.hadoop.io.MapWritable@a565aa59
5	org.apache.hadoop.io.MapWritable@fd426456
6	org.apache.hadoop.io.MapWritable@51a5ef6
7	org.apache.hadoop.io.MapWritable@556386e
9	org.apache.hadoop.io.MapWritable@5563878
10	org.apache.hadoop.io.MapWritable@556386c
11	org.apache.hadoop.io.MapWritable@5951fdd
```

I couldn't detect if the problem is in Map or Reduce methods.
Refactor of nextToken method. Not tested on D&G Indexer yet.
close issue #23
Merge pull request #28 from tomasdelvechio/iss23

Iss23