added ccache, cflow, cgdb, NASM, Yasm

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>
whitespace & header improvements

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>
Merge branch 'contrib_assemblers_build_debug' of github.com:fgeorgatos/easybuild-easyconfigs into contrib_downloaders_HPC