This change is done to reduce ambiguity in some cases;
the previous intention has been to ease navigation when
staying in a particular directory, now it's been changed
in favour of convenient toplevel `git grep' in fact.

Both variants have their pros and cons, I just find myself
leaning to this one by now hence the commit.  Feel free to
provide constructive criticism :)

Some path-related bitrot has also been fixed while at that.

These have been proofread somewhat to correspond
to the current state of affairs; a missing one
was added for fonts feature.

The script hook naming advice and "+name" puropose explanation
seem to have been missing.

Thanks both drool@ for his mild frustration with the current
documentation as well as Greg Kroah-Hartman, Heikki Orsila
and Neil Brown for http://lwn.net/Articles/504814/ -- the docs
should really emphasize *why* something is done, not *how*,
as the "how" part is better documented with the code itself
(that doesn't mean that "the big picture" isn't needed).

It looks like the intermediate targets aren't all equal:
some define a finished feature while some create a common
lower level piece of configuration.

Let's do shortcuts for the former so that a distro line can be
more terse and descriptive; help targets in features.in/ tweaked
accordingly.

These are gone for now, this fix should have been done before.

doc/variables.txt was missing the already-existing BUILDLOG
variable description, and ARCHES got added during multi-target
toplevel rewrite.  Other minor fixes come as appropriate.

The features might get copy-pasted (or even copied-and-pruned)
when initialized; there's an unneccessary duplication of the
function name in the line adding it to FEATURES list, thus
prone to being forgotten and causing some havoc later on.

It was wrong in the first place but tackling this with some
double-colon rules ran into terminality issues, and further
tortures were considered unneccessary.

The current solution isn't perfect (no completely transparent
function name registration upon corresponding target being called)
but at least it is an improvement...

It appears that features.in/Makefile functioned a bit
differently by now than was described back then: after
loops and pushds got rearranged for robustness, it stopped
to pick up a cleanup feature tagged script.

That particular script is now better de-tagged and simply
placed as a script to be merged into install2 subprofile.

The tagged scripts still require a bit more comprehension
to understand the use cases (e.g., do we need per-subprofile
tagged script subdirs or just a toplevel one should be looked
at, with script names telling where to put them).

README used to mix up subprofiles and features; fixed.

- toplevel README received some long-needed refactoring
  + lowlevel detail moved, well, to lowlevel READMEs
- reflected more thoroughly that m-p is not about distros anymore
- dropped features.in/00example/README.en: it's already out-of-date
  a bit, and there's no perceived need in thorough English docs so far
- wiki article got split into parts and somewhat rewritten, links updated
- mv doc/{CodingStyle,style.txt}

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)

From now on a feature can contain this tree:

.
+- scripts.d/
+- image-scripts.d/
`- tagged/
   +- scripts.d/
   `- image-scripts.d/

...per subprofile part or in its root -- the latter one
gets merged into toplevel directory responsible for the
final image build.

NB: autoselected tags include only subprofile names
    (or both parts, for complex subprofiles) --
    this is highly prone to change yet!

Introduced support for hooks to be added to every
derivative substage of a "base" stage (think stage2/*).

Specific hooks for e.g. stage2/live would live in
features.in/*/live/*scripts.d/ while generic for stage2/* in
features.in/*/stage2/*scripts.d/

reword 'em, structurize 'em, facelift 'em too

ToC:
- introduced doc/
- features.in/00example/
- READMEs and TODO for more
- code comments clarified

Some unrelated minor fixes bundled either.