timespec UPDATE reworked time functions

merged some time functions in order to be able to directly get some time in the future with a single function call
instead of having to get the current time and then add some time to it, also created a new function, which returns
the difference from the current time so that it can be put into condition statements instead of having to get the
current time and then get the difference.
diff --git a/src/io.c b/src/io.c
index 352a5f3..e3a57b0 100644
--- a/src/io.c
+++ b/src/io.c
@@ -92,7 +92,7 @@
     size_t readd = 0;
     ssize_t r = -1;
     int fd, interrupted;
-    struct timespec ts_cur, ts_inact_timeout;
+    struct timespec ts_inact_timeout;
 
     assert(session);
     assert(buf);
@@ -105,8 +105,7 @@
         return 0;
     }
 
-    nc_gettimespec_mono(&ts_inact_timeout);
-    nc_addtimespec(&ts_inact_timeout, inact_timeout);
+    nc_gettimespec_mono_add(&ts_inact_timeout, inact_timeout);
     do {
         interrupted = 0;
         switch (session->ti_type) {
@@ -211,9 +210,8 @@
             if (!interrupted) {
                 usleep(NC_TIMEOUT_STEP);
             }
-            nc_gettimespec_mono(&ts_cur);
-            if ((nc_difftimespec(&ts_cur, &ts_inact_timeout) < 1) || (nc_difftimespec(&ts_cur, ts_act_timeout) < 1)) {
-                if (nc_difftimespec(&ts_cur, &ts_inact_timeout) < 1) {
+            if ((nc_difftimespec_cur(&ts_inact_timeout) < 1) || (nc_difftimespec_cur(ts_act_timeout) < 1)) {
+                if (nc_difftimespec_cur(&ts_inact_timeout) < 1) {
                     ERR(session, "Inactive read timeout elapsed.");
                 } else {
                     ERR(session, "Active read timeout elapsed.");
@@ -227,8 +225,7 @@
             readd += r;
 
             /* reset inactive timeout */
-            nc_gettimespec_mono(&ts_inact_timeout);
-            nc_addtimespec(&ts_inact_timeout, inact_timeout);
+            nc_gettimespec_mono_add(&ts_inact_timeout, inact_timeout);
         }
 
     } while (readd < count);
@@ -363,8 +360,7 @@
         goto cleanup;
     }
 
-    nc_gettimespec_mono(&ts_act_timeout);
-    nc_addtimespec(&ts_act_timeout, NC_READ_ACT_TIMEOUT * 1000);
+    nc_gettimespec_mono_add(&ts_act_timeout, NC_READ_ACT_TIMEOUT * 1000);
 
     if (!io_locked) {
         /* SESSION IO LOCK */