Support sub dependency in a package

[katat]

When it is a lib dependency, it now assume all the code written in the lib.no.

It would be better if it allow the lib.no to instruct processing of other files.

For example, given lib.no:

use comparator;
use bits;

Then the compiler can look for the comparator.no and bits.no files in the package folder, and include them to be part of pipeline, instead of only taking care of lib.no

[mimoo]

note that maybe going the golang way would be interesting? (any .go file under the same folder is accessible without importing, like it's all part of the same file)