Treat '--speclj' as an alternative help option

[arlandism]

My attempt at tackling #102.

I wanted to remove the "help" option altogether, but didn't want to risk deprecating existing functionality. Given that Leiningen hijacks the "help" flag, is there another way that it could be used? If not, then we can kill it.

It's also worth mentioning that according to Leiningen's plugin docs you should be able to attach ^:pass-through-help metadata to your defined task to implement this workaround; this didn't work for me for some reason.

[arlandism]

@trptcolin confirmed that he got the ^:pass-through-help approach to work, but it looks like it requires lein 4+. I could add the metadata here for those that are using a newer version of lein, if that's desired.

[trptcolin]

Thanks!