Include -coverpkg=./... by default

[cdennison]

I tried using this tool to get a coverage report similar to goveralls but the lack of the "--coverpkg"
arg caused it to give a much different result. You can see goveralls is using --coverpkg here:
https://github.com/mattn/goveralls/blob/master/goveralls.go#L124

I suggest that you make this the command because I would guess that most people seeking multi-package coverage have package that depend on each other and this is what they want. Otherwise the results are confusing because it says you have no coverage when you really do.
go test -covermode=count -coverprofile=profile.coverprofile -coverpkg=./...

[deankarn]

Hey @cdennison an interesting perspective, I've always looked at coverage at the repository/project level and not the entire program, mainly because many packages that you use, you can't control the test coverage.

I am definitely open to adding support though, my time is just extremely limited right now though. I will try to add, but any help anyone can provide would be great! 👍

[cdennison]

@joeybloggs - looks like you recently added support for arbitrary flags so I just updated the README in PR #27 for how to do this if you need it.