Improved documentation and install instructions

[missinglink]

The documentation is currently a bit thin. In order to reach a wider developer audience and attract outside contributors, it would be beneficial to add the following to the readme:

• Project Summary
• Architectural Overview
• Installation Instructions
• Spatialite Primer & Compilation Guide
• Overview of the modules:
  • Place
  • Geometry
  • Shard
  • Hierarchy
  • Property
  • Spatial Relationship
  • Point in Polygon
• Running Tests
• RESTful API
• Demo App