Begin conversion to an instance-based framework

1. Turn Db into a standard base class, instead of an abstract singleton
2. Change the PostgreSQL adapter to work as an instantiated class
3. Remove Db references from Sql, since it has no access to
   instantiated adapters.

Ran tracking setup/teardown in Pry. No tests were run.
Formatting
Implement [] for PostgreSQL; pass adapter to task definition
Add adapter-specified task names, dependency resolution
Fix bad equality on identical Times by using DateTime
Comments
Make the Greenplum adapter instantiatable
Comments
WIP rake tasks run but tests fail
Fix Db, rake task tests; Time instead of DateTime

Tests db_spec and test_rake_table_task pass.
Switched back to using Time instead of DateTime for comparisons,
although Table still uses DateTime to store stamps internally.
Fix table_spec tests
Fix sql_spec tests; add adapter helper method
Merge branch 'datatask' into gemify

Replace the singleton Db model with an explicity declared adapter for
each data source/sink.
Rename directories and files
WIP rename table to data everywhere, persist Postgres connections
Break connection persistence into a module
Add gemspec
Readme
Merge branch 'datatask' into gemify

Rename tabletask -> datatask, add connection persistence