Updates installation instructions

* Snapshot schema is no longer needed
* Osmosis is built via gradle (not ant anymore)
* The osc diff file import was missing the `gz` suffix
* `tiler/owl_tiler.rb` is deprecated. Use `scripts/tiler.rb` instead

This is not sufficient to run OWL yet, but we'll get there.
Merge pull request #21 from thiagoarrais/update-instructions

Updates installation instructions
Replaced installation instructions with a link to the wiki.
Docs moved to the wiki.
Updated the main page.
Remove GeoJSON strings from change properties when generating JSON - they belong in GeoJSON features.
#20 Dropped the parallel gem (caused some slowdowns), reconnect to Postgres every 1000 changesets.
Limit aggregation to zoom level 12 and above.