Added .swp files to gitignore
Now use submodules instead of only direct classes.

Simplifies the module initializer.
Added the public `errors` module.
Added a bit of missing info in README
First version of the `builder` module.

It should be accessed from the `builder` property of a Connection
object.

Includes a test unit for the Builder class.
Small corrections

Missing docstring and bad-named property.