This commit updates the libcharset submodule to incorporate the
autotools-ification that I just pushed to that subproject, and builds
on it by replacing Halibut's own makefile system similarly with an
autotools setup.

The new Makefile.am incorporates both of the old Makefile and
doc/Makefile, so a single run of 'make' should now build Halibut
itself and all the formats of its own documentation, which also means
that the automake-generated 'make install' target can do the right
thing in terms of putting an appropriate subset of those documentation
formats in the assorted installation directories.

The old Makefiles are gone, as is release.sh (which is now obsolete
because autotools's 'make dist' doesn't do anything obviously wrong).
The bob build script is comprehensively rewritten, but should still
work - even the clang-based Windows build can use the
autotools-generated makefile system, provided I do the libcharset
build with a manual override of bin_PROGRAMS to prevent it trying to
build the libcharset supporting utilities (which are not completely
Windows-portable).

A long time ago, it seemed like a good idea to arrange that binaries
of Halibut would automatically cease to identify themselves as a
particular upstream version number if any changes were made to the
source code, so that if someone made a local tweak and distributed the
result then I wouldn't get blamed for the results. Since then I've
decided the whole idea is more trouble than it's worth, so I'm
retiring it completely.

[originally from svn r10254]

into a subdirectory of `halibut'. It wasn't very good anyway (since
it insisted on loading via an unauthenticated svn:// URL). The
Halibut makefile now expects _either_ a subdir `charset', _or_ a
directory called `charset' as a sibling of `halibut', and will work
with the first of those that it finds. A new release script arranges
to provide the former in source tarballs (so that building if you're
an ordinary user is just as simple as it always was).

[originally from svn r4808]