Rewrite from scratch serial.c
Fix wrong filename in read_file.
Fix bug in parse_node_descr_to

Nodes with one of the adiacency lists empty were not correctly
initialized.
Fix behaviour of node_init and node_new

Now the two functions will correctly initialize to NULL arrays of
neighbours of size 0.
Reimplement node_new and node_delete

Reimplemented both functions by means of node_init and node_free,
to avoid code duplication.
Update documentation of node_init
Add test cases

Found a bug: we should trim the description string of leading and trailing
whitespaces befor parse it.
Fix bug in parse_node_descr_to

Now lines not ending with a whitespace are correctly parsed.