@feelpp/lrz spread logfiles into subdirectories, basically every 200 process
id a new directory is created to store 200 logfiles
0-199, 200-399, ... 
Only the process id such that rank % 200 == 0 create the directory
and we have only 200 process writing in the same directory at the same time.
This follows the guidelines from 
https://www.lrz.de/services/compute/supermuc/filesystems/gpfs-usage/index.html#GPFS%2520Usage
update issue #161
now interprocessfaces(mesh,j) returns the faces shared between current subdomain/process
and subdomain/process j
interprocessfaces(mesh) returns as before all interprocess faces
added some use_count() to track down the leak
update issue #161
added example, not yet fully working