Rename vtkm/Algorithms.h

vtkm/Algorithms.h is too easy to confuse with vtkm/cont/Algorithm.h, and these serve very different functions. Besides, vtkm/Algorithms.h is not very descriptive of what is in

As of this writing, vtkm/Algorithms.h only has functions related to searching, so I recommend renaming this file to vtkm/Search.h.