Build CPC projects out-of-source

[cpcitor]

Currently, CPC applications are built "old style", "in source": build artifacts land in the same tree as source files.

This clutters the source directories with generated files, generates false positives when searching for text in source files.

It would be better to build CPC applications out-of-source. This would expand also to asset compilation (modern graphics file format to CPC file formats, etc).