* Added pcl::Histogram<N> preprocessor sequence up to N=25.
* Defined some point type sequences that extend existing ones with
  histogram types.
* Changed PCLP_INVOKE_WITH_* macros naming scheme for new sequences.
* Simplified PCLP_INVOKE_WITH_* macros to use a common internal macro.
* Updated conversion function templates to explicitly handle array
  types instead of pointers.
* Added CopyToCloud and CopyFromCloud to converter classes to loop over
  a single array at a time.