3.1.6

Features:

• Add ifort and ifx support (@jgonzac)
• Add ftnfe support (@inaki-amatria)
• Add LLVM's flang support (@ruifm)
• Add xgcc and xg++ support (@wataash)

Bugfixes:

• citnames: allow pre/postfixes to cc & c++ compiler calls (@jan-krieg)
• citnames: Add missing stdlib header (@ruifm )
• cmake: Add BUILD_ALWAYS to ensure BearSource rebuilds (@inaki-amatria)