Multiple databases v2

[calebhearth]

Add quite a bit more testing to the multiple databases feature, especially
around configuraiton, definition, and statement routing. Introduce a new
FakeAdapter class to let us test against a non-Postgres adapter without having a
dependency on any of the various actual adapters out there (we love you, but we
don't want a cyclic dependency!)

• Rework the new README changes to somewhat closer match the cheeky style of the
  original.
• Fix array handling for migrations_paths. Rails lets us define a
  :migrations_paths key that can be an array or a string in database.yml,
  and we previously ignored the possibility of that being an array. New
  functionality matches what Rails does.

Introduce configurable view paths! I'm hopeful that a lot of folks will be happy
with this. You can configure this with views_paths in database.yml and it
should default similarly to how migrations do to db/<database_name>_views/ for
non-default databases.

Fix: #291
Fix: #380
Fix: #261
Resolves: #402
Closes: #451

[calebhearth]

@dnamsons @leoplct @joshfester Would you like to give this a shot for the multiple dbs and/or adapters implementation?

@sullerandras @smdern @coding-chimp @MarcReniu @tomasc @huarmenta @vladimirtemnikov @nathanpalmer @jdno @shageman @hlascelles and probably others, this may also get us closer to some of the various Engines and configurable db/views paths needs so I'd love to get input on that as well!