Added function to calculate absolute value of ulm2

Samo Penic

2018-06-26 0661f62a1a4b5bc87310421d198e7df8538c7363

 src/io.h

@@ -72,7 +72,7 @@
 *   @param *text is a description line (max. 255 characters) to be included in the file
 */
ts_bool write_vertex_vtk_file(ts_vesicle *vesicle,ts_char *filename, ts_char *text);
ts_bool write_vertex_xml_file(ts_vesicle *vesicle, ts_uint timestepno);
ts_bool write_vertex_xml_file(ts_vesicle *vesicle, ts_uint timestepno, ts_cluster_list *cstlist);
ts_bool write_master_xml_file(ts_char *filename);
ts_bool write_pov_file(ts_vesicle *vesicle, char *filename);