Skipping empty strings

[edemaine]

Here's a small idea for Hera optimization: skip matching the empty string literal "". We use this ~70 times in the Civet grammar, mostly for declarative rules, which I imagine get hit a lot (you probably know better).

Given that it always matches, we shouldn't need to build/call $L at all. I think this optimization could be in compileOp but I haven't understood this code yet to know how to try it.

[STRd6]

I think it's a good idea in principle but it is made difficult by the need to aggregate handlers.