add target html and gallinahtml

also add html folder to .gitignore so generated doc is not added to the repo

merged

Merged, thanks!

I do not understand the point. All targets are forwarded to the Coq Makefile, so this should already work anyway (just like e.g. "make quick"). And indeed make html works fine in Iris with the old Makefile.

@benoit Could you explain why this is necessary? Otherwise I suggest to revert the change.

@jung indeed I didn't see this (nor did I know that it was possible).

# Forward most targets to Coq makefile (with some trick to make this phony)
%: Makefile.coq phony
	+@make -f Makefile.coq $@ 

So I do agree that this is not necessary.

All right, I will revert the changes to the Makefile but keep the .gitignore change intact.