Bump deps on conduit to be >= 0.5.3.

These libraries assume that Data.Conduit re-exports
MonadBaseControl.
Remove dead CPP code from persistent-sqlite.
Simplify db.
Allow NULLables on uniqueness constraints.

They're supported by the SQL standard and are useful.
Force the use of a "!force" attribute for NULLables on uniques.
New Checkmark data type.
Add support for "nullable" attribute.
Merge pull request #106 from meteficha/unique-on-null

Allow NULLables on uniqueness constraints.
Merge pull request #107 from meteficha/checkmark

New Checkmark data type, new "nullable" field attribute.
Version bumps
PersistField Instance for Lazy Text (#98)
Create tables before adding constraints (#24 and #32)
PostgreSQL default port (#60)
Version bumps
fix compiler warning of unused name
fix test warnings
use raw MongoDB pipes: allows changing the database
use default MongoDB port from MongoDB package
improve documentation
minor version bump