Merge pull request #28 from chuckpreslar/v0.4

v0.3.3
Merge pull request #29 from chuckpreslar/v0.4

PostgreSQL parameterization support.
Merge pull request #30 from chuckpreslar/v0.4

Replace `engine` and `Engine` on managers in favor of `adapter` and `SetAdapter` respectively.
Merge pull request #31 from chuckpreslar/v0.4

v0.3.4
Package documentation.
Add common SQL type and constraint constants for table creation and alteration.
Remove unnecessary "tree" directory as it represents no Go package.