Minor modifications to xx21.f90
Minor updates to program xx16.f90
MINOR Change: Removed binary executable xx21
MAJOR Change: Added new development programs xx20 and xx21.
MINOR Change: Removed tool "convert_endian" from default build.
Added build file for Knights Landing on ARCHER.
Added patch to gather_scatter.f90 provided by Nicolas Gruel that seems to fix OpenMPI issue.
Minor modifications to program/dev/xx1