replace _ with - in option names

[lexicalscope]

its common to have "-" in options names, which is not allowed in java; replacing _ with - in option names might be a neat way of solving this issue; although it cause trouble for anyone using _ at the moment and make it harder to get _ to work (would have to specify an explicit option name string). But its so much more likely for people to want - in the option that it might be worth it.