xbps 0.2

This version has major changes compared to previous version (0.1), the following is
a brief list for the most important changes:

* Added support to replace a package (or packages) providing the same functionality
   by some other new package. A build template can use the "replaces" variable that
   accepts a list of packages.

* The utilities now are also installed statically linked (with .static extension) to avoid
   some chicken-egg problems while building packages in the chroot.

* Fixed a serious bug when an indirect dependency couldn't be found in the repository
   pool, resulting in an endless loop.

* Fixed a serious bug that resulted in unpacked packages with wrong permissions.

* Fixed a bug where updating a package marked as "essential" wasn't removing its
   requiredby entries, thus duplicating them.

* xbps-bin: renamed "files" target to "show-files".

* xbps-bin: "show" target no longer prints the required run dependencies, rather two
   new targets have been added: "show-deps" and "show-revdeps", the latter to print
   the packages that are using it.

* xbps-src: libtool archives and empty dirs are removed by default, can be overriden
   by using the "keep_libtool_archives" and "keep_empty_dirs" variables, respectively.

* xbps-src: executables and libraries are stripped off by default, can be overriden by
   using the "nostrip" variable.

* xbps-src.conf: a new option have been added: XBPS_FETCH_CMD. It's used to fetch
   distfiles while building packages. Please note that it's copied into the chroot, so
   it should point to a command with no deps other than libc (or use a static binary).

* Multiple fixes and changes thorough the code, stability has been improved.