new: hot reload functionallity

[DonutEspresso]

Continuation of #13.

[DonutEspresso]

@yunong this might be a good place to help out with - this would be a huge win for devprod immediately. Open questions:

• should the hot reload configuration be an enroute schema configuration or a runtime option when you call install? (I prefer latter)
• are the typed errors a major breaking change? (I prefer yes)
• what's a good way to add a test for this? (add a test that changes the response payload and verify it that way?)

Also need to update README

[yunong]

@DonutEspresso Landed tests and docs.

[DonutEspresso]

Wah wah, fs-extra breaks on node4 due to some ES6 syntax. It looks like a dev time dependency only, are there other alternatives? Or we can make this a breaking change for enroute by dropping node4 support?

[yunong]

Already dropped v4 support ;)

[DonutEspresso]

lgtm. is this a new major version then?

[yunong]

Looks like it