These were excluded to separate files, because Mark was thought to make
use of them.

The Validator also contains information about supported attrs. Currently
they can't be initialized by a spec. Also it can only be queried whether
an attr does exist at all and not whether it is supported in combination
with a specific tag. The tests are missing.

There is a method to add a set of tags to a validator on initialisation.
First this removes a user application from the burden of maintaining the
html spec and also is more performant, as a lot of tags are to be
inserted at once, so there aren't multiple allocation calls.
As the validator needs the tags to be in order, the tags must be sorted
on insertion. Of course it would be easier for the code, if the tags
were already in order, but first there could be easily a mistake and
second sorting the tags by an algorithm allows the tags to be specified
in a logically grouped and those more maintainable order.
For the sorting, insertion sort is used. Of course it has a worse
quadratic time complexity, but in a constructor, I wouldn't introduce
the overhead of memory managment a heap- or mergesort would introduce
and in-place sorting is also out, because the data lies in ro-memory.
Thus I choose an algorithm with constant space complexity. Also the
'long' running time is not so important, as the initilization only runs
at startup once and the tags are not likely to exceed a few hundred so
even a quadratic time isn't that bad.

Double inclusion accompanied with macro guards are a bit ugly in
comparison to a separate file.

The marks are now allocated and the allocated, where appropriate.

A mark will be used to point to a specific location inside of a text.
Currently it can't do anything and isn't even used.

While it would be preferable, it doesn't seam to be possible to abstract
over the internals of text_segment. That's why only some basic
functionality is moved, but whether more is to follow, is not known yet.

The basic functionality to implement all abstract methods is added. This
means, that TextFragment can be instantiated, but it can't do anything
useful yet.

They are used later, if another internal module wants to use them.

This is used later, if another internal module wants to include the
declaration.

When used with care, it is possible to bypass many strdup calls.
To also save the instructions for the call, which are a lot of overhead
now, link time optimization is turned on. (-flto)

The structure SH_Attr implements an HTML Attribute.

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

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.