Should fail on unrecognized flags

[glasserc]

Per #136, it's possible for a user to be passing the --debug flag to elm-live in an incorrect way, in which case it becomes silently ignored. Flags that elm-live doesn't recognize should probably cause a failure so that it's obvious what the problem is. This is especially helpful for those of us migrating from versions of elm-live that did in fact recognize --debug.

[wking-io]

This is a good recommendation! I will be happy to add this! What if instead of failing there was a warning that listed all unrecognized arguments along with a message along the lines of:

Warning: Flags below were not recognized. If any of these are flags for elm make you will need to move them after the --. Otherwise you can reference the docs for help: https://github.com/wking-io/elm-live

[glasserc]

Sorry for the delay! This email got routed to "Spam" somehow. I don't have a strong opinion about whether unrecognized arguments should be fatal or merely a warning, but I would point out that most other programs treat unrecognized arguments as fatal, including notably elm make and elm-format. But I'd be happy to see either a warning or an error.