Updated tutorial.
Merge pull request #15 from lossyrob/tutorial

Updated tutorial.
Update README.md
Add in some vector docs
Move to overviews section
Split getting started into 'Overviews' and 'Getting Started'
Merge pull request #16 from geotrellis/topic/vectors

Add in some vector docs
Merge pull request #17 from geotrellis/topic/reorg

Split getting started into 'Overviews' and 'Getting Started'
Fixed capitalization of GeoTrellis on front page.
Updated web tutorial link to new rendering overview.