Added early return option to next function that allows returning timestamp of next occurence instead of delay.

crontab/_crontab.py

diff --git a/crontab/_crontab.py b/crontab/_crontab.py
index fd7f0ca..4d227bb 100644
--- a/crontab/_crontab.py
+++ b/crontab/_crontab.py
@@ -422,7 +422,7 @@
             attr = attr() % 7
         return self.matchers[index](attr, dt)
 
-    def next(self, now=None, increments=_increments, delta=True, default_utc=WARN_CHANGE):
+    def next(self, now=None, increments=_increments, delta=True, default_utc=WARN_CHANGE, return_datetime=False):
         '''
         How long to wait in seconds before this crontab entry can next be
         executed.
@@ -479,6 +479,9 @@
             "crontab: %r\n" \
             "now: %r", ' '.join(m.input for m in self.matchers), now)
 
+        if return_datetime:
+            return future
+
         if not delta:
             onow = now = datetime(1970, 1, 1)