Added support for ExtededData (XDATA).

All the data described in http://www.autodesk.com/techpubs/autocad/acad2000/dxf/index.htm are parsed and the 1002 block goes to a list of attributes.
The SimpleFeature returns a Map with the parsed data and with a list with 1002 attributes
Create readme

Initial readme
Update formatting
Merge pull request #189 from sosimple/master

DXF Parser Extended data support