* Big rework of Assign.h:

** Much better organization
** Fix a few bugs
** Add the ability to unroll only the inner loop
** Add an unrolled path to the Like1D vectorization. Not well tested.
** Add placeholder for sliced vectorization. Unimplemented.

* Rework of corrected_flags:
** improve rules determining vectorizability
** for vectors, the storage-order is indifferent, so we tweak it
   to allow vectorization of row-vectors.

* fix compilation in benchmark, and a warning in Transpose.

bench/benchmark.cpp

@@ -1,5 +1,5 @@
 // g++ -O3 -DNDEBUG -DMATSIZE=<x> benchmark.cpp -o benchmark && time ./benchmark
-#include <Eigen/Core>
+#include <Eigen/Array>
 
 #ifndef MATSIZE
 #define MATSIZE 3