Added pack command
Fixes
Some extra tests
Fix. Used java.source and not javac.source, also for other
properties.
#473 close. Flattened properties are not completely expanded.
Properties that start with a minus sign are not processed, so they still contain the macro
Properties that start with an '_' are not included at all.

Adapted the comment and added a new method that can be used to do the full expansion
Added more threads to the default thread pool
Some fixes in the compile code
- debug is currently a boolean, can now ALSO set the debug option
- Projects without sources caused errors
Diagnose (impossible, but hey) errors in loading the defaults
- Updated debug to show the flattened properties
- Some weekend experiments with parallel build