beremiz

SVGHMI: add support for "enable expressions" with arbitrary variable name assignment.

HMI tree paths can be prefixed with a variable name "@name=/MY/HMI/VAR"
Widget declarations can end with a "#" followed by a JS expression that refers to name given to variables.
Widget is disabled if expression's result is false.

Commit includes some more-or-less related generated code refactoring, that should simplify extending widget's variables attributes.
BEREMIZ_OBJS = $(BEREMIZSRC:.c=.o)
all: warn some_binary
@echo "*** all done ***"
warn:
@echo "*** Sample Makefile, does nothing ***"
some_binary: $(BEREMIZ_OBJS)
@echo "* Would link $^ -> $@"
%.o: %.c
@echo "* Would compile $< -> $@"