Add ACME HTTP-01 Challenge support

[elct9620]

For #26, make the HTTP-01 challenge supported.

TBD

• Should we make the HTTP-01 optional (disabled by default)
• Should we create HTTP-01 middleware when path start with /.well-known/acme-challenge/ or create it for all request
• Let's try to make a mock ACME server to test it

[kevinmcconnell]

@elct9620 I actually had a different implementation of this prepared, which I've now shipped.

Sorry for the overlap in our work here -- I would have had mine merged sooner, but was travelling over the weekend. But thanks for your contribution all the same!

[elct9620]

@kevinmcconnell

Thanks for your information. I checked the change and it is a better one. I
didn't check Service has a createMiddleware() method so that we can create a handler directly inside it.