Trim down README and move more detailed information into docs directory
Add a file explaining how to do basic geospatial analysis with osm2pgsql

Based on an unpublished blog post I never finished off
Add a paragraph on exporting from an osm2pgsql db

osm2pgsql can be part of a useful toolchain for generating shapefiles,
but little is documented about this, so this adds a basic paragraph.
Add some documentation on the pgsql backend
Add a lengthy document on osm2pgsql usage

osm2pgsql has a *lot* of command-line options
Add a (very) basic file on gazetteer
Merge pull request #179 from pnorman/docs

Readme and docs rewrite