Updated filemanager to use dynamically allocated strings

converted filename to dynamically allocated string
created cstr_helper

src/outfile/CMakeLists.txt

@@ -22,7 +22,8 @@ set(CMAKE_INCLUDE_CURRENT_DIR ON)
 # configure file groups
 set(EPANET_OUT_SOURCES  src/epanet_output.c
                        ../util/errormanager.c
-                       ../util/filemanager.c)
+                       ../util/filemanager.c
+                       ../util/cstr_helper.c)
 
 
 # the binary output file API