Geo library proofing

Summary:

• Documenting default value of 6 for the counf parameter of the method GeoPointPolarZ::calculate_section($angle, $count)

• Tables were hardcoded in GeoPlace model class' SQL queries

Test Plan: Trivial edits

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: http://code.zed.dereckson.be/D8