Notably, pass around the location of the xcvb-program we create in the cache.

* Use define-command to define and register a command
* Introduce the notion of workspace to store intermediate and target files.
* Update Makefiles for new intended output paths

* extract fasl type from target:
 at least lispworks depends on pathname type and its fasl type varies!
* rucksack not available on clisp (and needed fixes; see our xcvb repo of it)
* accept compile-file failure semantics of clisp
* suppress duplicate entries for a directory in the source-registry:
 The first one wins, with its recurse and exclude flags.
* fix hello and test/runme
* fix various option parsing mistakes

	settings known to xcvb or the individual value of a single one.
Change the default object-directory location to be
	$HOME/.cache/xcvb/common-lisp/<lisp-implementation-version>/
Added format! in driver.lisp to help with debugging and forcing output.
Debugged CMUCL support in driver.
Fixed implementation-identifier support in extract-target-properties.
Allowed Makefile in example-1 to parameterize on lisp implementation.
Refactored how option-specs are specified for command line options.
Removed dead code paths from simple-build backend that dealt with
	"xcvb.mk" and the makefile output file.
Muffled warnings when loading asdf.
Added target-asdf-version setting which you can query with show-settings.
Started DONE.rest

TODO for ECL: distinguish linkable object files from loadable shared objects.

Give proper semantics to resolve-absolute-module-name and resolve-module-name.
Make the hello example work properly.
hello now uses the generate functionality to extract version from parent XCVB.
Have log-format do fresh-lines for you.
Make sure builds are only interned once.
Recognize that builds may be invalid because of inherited conflict.

Easy functionality: version, ssr and a2x work.

* The Makefile has a pre-release-test target, so no need to commit
 "yet another attempt at auto-validated release" anymore --
 I will test whether the code I have passes muster before committing.
* error out early if XCVB_OBJECT_DIRECTORY wasn't configured.
* Fixes to the regressions in the non-enforcing backend that had been
 made to implicitly rely on a previous run of the enforcing backend.
* Factoring out common option handling.
* Removing cruft from previous over-design of the computation class.
* Many thanks to Attila Lendvai for testing.

* start some test infrastructure for release
* make image mode the default in configure.mk, for the sake of CCL
* fix the forker package, bake a collection macro
* extract executable and image name from target lisp (when possible)
 in view of tthsum'ing it in the future.

* Introduce the world-grain abstraction as a step towards a farmer.
* A few important cleanups and refactorings.
* better hush the build

* xcvb-master: robustifying the reading of slave results
 (on a suggestion by Attila Lendvai) + doc updates
* xcvb repl shouldn't need you to export SBCL_HOME anymore.

* allow lisp modules with their own build-dependencies different from their parent.

* start of a forker and farmer
* better error message when you forget to make your dependencies a list
* doc update

* makefile backend bug: make was doing the wrong thing when a.fasl depends on b.cfasl
  which depends on b.fasl. Apparently, when b.fasl was recompiled, a.fasl wasn't recompiled
  until the next run of make; we ensure it will by having a.fasl depend directly on b.fasl.
* move code around: remove style-warning when loading master as lisp.
* have master explicitly support pathname arguments
 (though princ must have done the right thing already before then).
* more moving code around: move specific commands out of main.lisp.