Add the first vectorized add and add flags to use OpenMP SIMD pragmas.
Align the underlying array of Vector and add runtime switched between add and vectorized add.
Replace transform by vectorized_transform.

Replace initialize_val by allocate and clear_val by deallocate.

Add vectorization to changes.h
Merge pull request #109 from Rombur/branch_vectorization

Vectorization (SIMD) of Vector
Fix compilation of Vector when configured with PETSc

this was introduced in e5f7ade
Merge pull request #119 from tjhei/fix_petsc_compile

Fix compilation of Vector when configured with PETSc