This is quite a large-scale change since mkimage-profiles got used to
baking distributions over the last year, and virtual environments are
quite different, so e.g. image.in/Makefile had to be split in two with
the main part of it moved into features.in/iso/lib/.

Short overview:

- features.in/Makefile: lib/ support
  (supporting VE images requires dynamic modifications
  to image.in/Makefile before starting the build;
  the most natural way to achieve that seems to use
  features mechanism along with makefile include dir)

- packaging format related part moved into features.in/pack
  (should be better prepared for diversity either)
- features.in/iso renamed to features.in/build-distro
- features.in/ve  renamed to features.in/build-ve
  + NB: these could not be merged as e.g. features.in/build
    due to completely different script hooks

- lib/image.mk renamed to lib/build.mk
- image, config, log postprocessing moved downstream
- added a sort of a topping in the form of lib/sugar.mk
- assorted style fixups (like ifeq usage)

- clean.mk: reliability fix (the problem was observed by Oleg Ivanov
  and me too but finally it did get the attention quantum)

- reviewed, updated and extended docs
  + QUICKSTART: should be[come] a step-by-step guide
    (thanks Leo-sp50 for prodiving feedback)

- better *_LISTS printout
- somewhat cleaner .base comments
- more comprehensible git log messages
  + special handling for complex subprofiles
  + no need to commit build.log ;-)

This looks a bit weird (two subprofiles become a bit more
tightly coupled) but in fact install2 does depend on stage1,
and if stage1 doesn't create squashcfg.mk then install2 is
just fine with defaults (provided they fit the installer kernel
used).  A proper mkimage test infrastructure might be handy though.

Also there:
- 01-initfs: partial cleanup (bootsplash is obsolete anyways)
- regarding 03-test-kernel's errorlevel test:
  if 0, 1 and 2 need to be distinguished, "!" MUST NOT be used
  as it negates so that 0 becomes 1 and the rest becomes 0