Update README for shared extensions schema

https://github.com/influitive/apartment/issues/135
Formatting
Use same logic as postgres adapter in postgis

This adds support for use_schemas = true as well as use_sql = true when
using the postgis adapter.
Merge pull request #150 from fphilipe/fix-postgis-adapter

Use same logic as postgres adapter in postgis
Merge pull request #141 from danelowe/development

Update README for shared extensions schema
Support latest version of activerecord as a dependency.
generalize rescuable exceptions
fix appraisals + add rails 4.1
fix 4.1 build branch
fix gemfiles for travis
update gemfiles for mysql2