Including source code into the documentation by default

[lvjr]

The documentation file xcolor.pdf doesn't include the source code. Although it is not hard to manually change some setting to add it, in my opinion it is still a better choice to include it by default.

[FrankMittelbach]

Most people appreciate it if a documentation doesn't contain huge number of page with source code. Which is why we started to split into foo-doc.pdf (or foo.pdf) and foo-code.pdf. Perhaps that should happen here too.