bpkg compatibility

[jwerle]

It would be nice if this were bpkg compatible !

Being able to do:

$ bpkg install orlin/batshit

Would be nice :]

bats is currently bpkg friendly

[orlin]

@jwerle batshit is nothing other that bats via npm. Its point is to test node cli scripts. I could make the batshit-helpers bpkg-installable if anyone wanted to load just that file for use in their bats tests, but I just copied those functions from another @sstephenson project and I imagine they may come with bats in the future anyway...