Added documentation of buildout:directory option.

Added support for extending configurations through multiple
configuration files.

Added command-line options to:

- Specify a configuration file

- Override configuration options

Renamed several options to use -s rather than _s.

option. The values are setuptools requirements and can have spaces in
them.

specified.

time. Rather, we generate in-line logic that pkg_resources would provide.
This means that apps that don't actually use pkg_resources themselves
don't end up running it and we don't need to implicitly include the
setuptools egg in the script path.  Of course, if an application does
use setuptools, then setuptools will be one of it's requirements and
will be included in the path.

Added the ability to control script generation.

this api.