C++ cleaning

The conversion was done from a top to bottom approach. Therefore a strong focus as been done on the user API. All the files should be checked and cleanup in a bottom to top approach in order to ensure that no C is remaining.

Files done:

• array
• cache
• cosmology
• definitions
• error
• fields
• hashmap
• header
• index
• inline
• interpolation
• logfile
• mapped_file
• openmp
• parameters
• parser
• particle
• part_type
• python_wrapper
• quick_sort
• reader
• time
• tools
• version