Added self dependency.

The Makefile now depends on itself, causing a rebuild of all files if the Makefile is modified.
Implemented ruter_stop_copy().

This function recursively copies a stop_t structure and all its fields, except from
its next pointer. A number of support functions was required: wstr_dup() copies a
wstr_t struct (required new function wstr_size() which returns the size of a wstr_t
and its content in bytes) and ruter_line_copy() which copies a line_t structure in the same manner as
ruter_stop_copy.