Fragment can be copied, either recursive (copying also all childs) or
nonrecursive (ignoring the childs, thus the copy has always no childs).
Adding the same element twice in the tree (graph) isn't possible, as
this leads to problems e.g. double free or similars.

The methods
- SH_Fragment_get_child (by index)
- SH_Fragment_is_child (non recursive) and
- SH_Fragment_is_descendant (recursive)
were added.

A Fragment can contain childs. When building the html, the childs html
is generated where appropiate.

SH_Text_append_string can be used to append a string to the text,
SH_Text_append_text can be used to append another text to the text.
SH_Text_join is a wrapper for SH_Text_append_text, but also frees the
second text, thus joining the texts to a single one.

A Fragment can output it's html. If there is an error the method aborts
and returns NULL.

Changing sefht_validator_test so that no memory leaks occur.

The space a Text has for saving the string is allocated in chunks. To
request additional space SH_Text_enlarge is called. If the requestad
size fits inside the already allocated space or is even smaller than the
current size, nothing is done. Otherwise a multiple of chunk size is
allocated beeing equal or greater than the requested size. The chunk
size can be changed by changing the macro CHUNK_SIZE in src/text.h. The
default is 64.
This adjustment is done automatically when a string is added.

Check in tests whether error really was written, by setting it to
undefined before each call.

This is a data type to deal with frequently appending to a string.

When a tag is made known to the Validator, which it already knows, the
old id is returned and nothing is added.
As this has to be checked by iterating over all known tags, a new helper
function is written for both SH_Validator_check_tag and
SH_Validator_register_tag: SH_Validator_get_tag.

Because we want also to test this function, we have to include
validator.c in the test file and override the static keyword by an empty
macro. It isn't possible any more to check for correct overflowdetection
by setting the index to UINT_MAX, because it will be iterated over all
data, thus raising an SIGSEGV when doing so. This is solved by filling
garbage unil UINT_MAX is really reached. As there would be an timeout
and it would fill RAM with around 40 GB of garbage, UINT_MAX is
overriden prior to inclusion of validator.c .

Validator serves as an syntax checker, i. e. it can be requested whether
a tag is allowed.

Tests are done using check, allowing to integrate the tests into the
Autotools.
Methods that are part of another unit, but are called in this unit
aren't tested as this would interfere with the idea of unittests. This
also applies for purely wrapper functions, where a call is passed to
another unit.