Provide a way to add hooks when using --require

[glenjamin]

A suggestion for a solution to #764

[tj]

would be nicer to get away from --require (so we can eventually remove it) and just require() like normal

[glenjamin]

I suppose i'm trying to avoid having an identical line at the top of every test - but it's not like that's particularly arduous.

[tj]

yeah, at the time I wanted --require just because I thought require('should') to grab a global was sort of awkward, but I regret adding it haha