Provide a debug option for generated code

[raner]

Occasionally, there are problems with the runtime-generated bytecode that Projo produces, for example, one might see an error message like this:

java.util.ServiceConfigurationError: bootstrap.Bootstrap: Provider natives.bootstrap.Bootstrap could not be instantiated
	at natives.IntegerTest.installBootstrap(IntegerTest.java:19)
Caused by: com.google.inject.CreationException: 
Unable to create injector, see the following errors:

1) [Guice/ErrorInjectingConstructor]: IncompatibleClassChangeError: Interface method reference: 'Id Something.id()', is in an indirect superinterface of False$Projo
  at False$Projo.<init>(Unknown Source)
  while locating False$Projo
  at Bootstrap$1.configure(Bootstrap.java:69)
  at Provider.booleanFalse(Provider.java:30)
      \_ for field booleanFalse
  at Bootstrap._addBinding(Bootstrap.java:122)

This vaguely suggests that there is something wrong with the implementation of the constructor for False$Projo, but the exact nature of the problem is hard to diagnose because there is no "source code" per se, and no .class file either. The generated bytecode only exists within the JVM.

It would be nice if there were a way to easily get hold of the class file for a generated type (e.g., by saving a copy in /tmp or some other specified location).

[raner]

For future reference: the debug property is called pro.projo.debug.path and must specify an absolute path to a folder where generated class files will be stored (e.g., /tmp).

From a Maven build for Projo itself this feature can be enabled by this command-line argument:

    mvn clean install -DargLine="-Dpro.projo.debug.path=/tmp"

This will result in debug classes to be saved, e.g., during test execution.

In a build for a downstream project that uses Projo directly from a Maven plug-in the command-line syntax is the usual:

    mvn clean install -Dpro.projo.debug.path=/tmp