Update express-unless with new types

[sylhare]

Hello @jfromaniello,

Here is a proposition to refresh the project in typescript, I have:

• Added a new UnlessRequestHandler type (so it can be used outside of this package)
• updated some variable name
• extracted the result into a method
• Use some smaller notation (like anonymous function and ternary operator)
• Return next() or middleware() to handle asynchronous behaviour

I was thinking Params could be named UnlessOptions but didn't want to make a breaking change there.

Let me know what you think

All tests are passing: