Implement initsingle_slist

Implement static initializer to init slist_t with a single
node (element).
Change signature of insertXXX_slist functions

The functions do no more check the next pointer to be NULL.
So the functions always succeed and simplifies implementation
of more complex functions which do not need to check errors
if they know for sure that elements which are inserted into slist_t
are not part of any other list.
Change retval of scannedtoken_utf8scanner to const

scannedtoken_utf8scanner(utf8scanner_t * scan) now returns
type "const splitstring_t *".
Make free_vmblock more robust

int free_vmblock(vm_block_t * vmblock) now works
also in the case where object vmblock is located
on the same page vmblock which is about to be freed.

Now pagesize_vm() must return a value >= 256.
So all functions can rely on the fact that a memory page
has at least 256 bytes.
Implement transCtoken_t

This type carries the information about a recognized
word (lexeme) of the trans-C programming language.

This type will be modified in the future to adapt to
the needs of a trans-C parser and scanner.