Source code regarding tags are exported to validator_tag.c and
validator_tag.h for better separation and integration of new features.

The Validator saves the tags as an array. Now also another information
is added, which slots aren't used currently to spare expensive calls to
realloc. This led to a mere reimplementation of the functions. Tags
can't be deleted by now, but the adding function supports reusing empty
slots. Also the reading functions have to determine, whether a slot can
be read or is empty.
The tests were adjusted, but are buggy, so they should be rewritten in
the future.

Additionaly some annotations for splint were added.

Instead of the trivial structure SH_Error, SH_Status is used. The name
was chosen, because error/status is set independently whether an error
has occurred. Beside the error type, it also contains the associated
errno and an error message. The error message is also printed, when it
is set. Generating error messages with variadic arguments is now also
supported.
There are also macros to check for a set status.

The exception handling was removed for the *_free methods, because they
can't fail predictably during runtime.

Unfortunately the compiler reports, that inside the macro set_status
printf may be called with NULL [printf (NULL)], although, this is
explicitly debarred.

The make process was restructured to create a library. For this libtool
is used to provide both static and dynamic linking. Also header
inclusion guards were introduced, to prevent clients of the library to
include some single file without including others. The types were
exported with forward declarations for better abstraction. When
compiling the library, the macro LIB_SEFHT_COMPILATION is defined and
symbol declarations are exported fully. For compiling the tests this
macro is also defined, as the tests not only tests the API, but also the
internal state, because a lot of errors couldn't be detected otherwise.