Fix memory errors

After https://github.com/openstreetmap/osm2pgsql/commit/d1b6c5e563e8eb9d836d97fad094f0a1b35f92ea#diff-a4a10b448709d2cc5dc0c85fb36a2b1c
the RAM cache size can be zero, but ``am_cache_nodes_set_sparse`` often accesses ``sparseBlock[0]``. It gives serious memory access erros and failures during testing (detected with Intel Inspector XE when fixing Windows builds https://github.com/openstreetmap/osm2pgsql/issues/17 ).

I am not sure the proposed fix is the best solution, but something should be done with this error.
constrain geometry check to way column

When more than one geometry column exists in a table, the sanity check
was failing when running osm2pgsql in append mode. This constrains the
number of rows and srid check to the way column specifically.
gazetteer: drop relations without way members immediately
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Based on an unpublished blog post I never finished off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
Support alt_name_* tags in output-gazetteer
Merge pull request #179 from pnorman/docs

Readme and docs rewrite
Merge pull request #176 from rmarianski/constrain-geometry-check

constrain geometry check to way column
Merge pull request #175 from alex85k/patch-1

Fix memory errors
gazetteer: ignore landuse without name

also fixes a tiny memory leak with landuses
make clean should delete files generated by protobuf