Add in new sections for loading, processing and saving

data.md: How to get data into geotrellis
output.md: What to do with your final result
processing.md: I have a raster, what can I do with it?

The rest of the files just have the page number updated
Whitespace cleanup
Merge pull request #6 from geotrellis/topic/update-getting-started

Add in new sections for loading, processing and saving