e2fsprogs: introduce script used to generate utf8data.h

e2fsprogs: introduce script used to generate utf8data.h

The mkutf8data program was written by SGI for the kernel. We integrate
it here, but it should be kept in sync with the kernel code, when
applicable.  The header generated by this script is also included in
this repository, such that we don't have to carry the UCD files too.
They are only necessary when the header has to be recreated (for
instance, to update the Unicode version supported)

The mkutf8data is not a dependency of utf8data.h because we don't want
the utf8data.h rule to be called after a make clean that would remove
mkutf8data.  It is simpler to call it from inside the rule, and make
sure we only trigger the utf8data.h rule if we really need to,
particularly if we decide not to integrate the ucd files in the tree.

The UCD files are not distributed along with this commit, but we add
information on how to fetch them.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>