Add a simple serialization mechanism.

The `Serializer<T>` class implements a binary serialization that
can write to (`serialize`) and read from (`deserialize`) a byte
buffer.  Also added convenience routines for serializing
a list of arguments.

This will mainly be for testing, specifically to transfer data to
and from the GPU.

test/CMakeLists.txt

@@ -288,6 +288,7 @@ ei_add_test(blasutil)
 ei_add_test(random_matrix)
 ei_add_test(initializer_list_construction)
 ei_add_test(diagonal_matrix_variadic_ctor)
+ei_add_test(serializer)
 
 add_executable(bug1213 bug1213.cpp bug1213_main.cpp)