implement file I/O

[jeffhammond]

PCosta said he uses this

[jeffhammond]

This is what is there now:

• MPI_File_open
• MPI_File_close
• MPI_File_delete
• MPI_File_set_size
• MPI_File_preallocate
• MPI_File_get_size
• MPI_File_set_view
• MPI_File_read_at
• MPI_File_read_at_all
• MPI_File_read
• MPI_File_read_all
• MPI_File_write_at
• MPI_File_write_at_all
• MPI_File_write
• MPI_File_write_all