Made alias_tensor take a default offset of 0 so you can easily use it to

reshape a tensor.

dlib/dnn/tensor.h

@@ -617,7 +617,7 @@ namespace dlib
 
         alias_tensor_instance operator() (
             tensor& t,
-            size_t offset
+            size_t offset = 0
         ) const
         {
             DLIB_CASSERT(offset+size() <= t.size(), 
@@ -642,7 +642,7 @@ namespace dlib
 
         alias_tensor_const_instance operator() (
             const tensor& t,
-            size_t offset
+            size_t offset = 0
         ) const
         {
             alias_tensor_const_instance temp;

dlib/dnn/tensor_abstract.h

@@ -680,7 +680,7 @@ namespace dlib
 
         alias_tensor_instance operator() (
             tensor& t,
-            size_t offset
+            size_t offset = 0
         ) const;
         /*!
             requires
@@ -701,7 +701,7 @@ namespace dlib
 
         alias_tensor_const_instance operator() (
             const tensor& t,
-            size_t offset
+            size_t offset = 0
         ) const;
         /*!
             requires