added description of Makefile include files for build configuration
fixed a crash when lines start with whitespace
also optimize single-bit "$mux" cells in pass "opt_const", added suggestions
for more optimizations
added one more suggestion to optimize MUXes in pass "opt_const"
added a TODO
keep $mux and $_MUX_ optimizations separate in opt_const
improved $mux optimization in opt_const
added optimizations for single-bit $eq/$ne with constant input to opt_const
Merge branch 'hansiglaser-master'