Deprecate returning false and friends in favor of promises

[dblock]

The change in #133 was backwards compatible, but we may want a major version change that supports only promises and just using:

Promise.resolve(handlerResult).then(res.send).catch(handleError);

We can also remove the return false functionality and make either returning a Promise or calling the callback required in order to send the response (or just call response.send() explicitly).

[ajcrites]

@dblock do we still want to support callbacks as well or can we purely support promises? This will also apply to pre/post.

[dblock]

I think a deprecation message should happen first, then a major version bump and only supporting promises with good documentation is 👍 for me.

[ajcrites]

Do we want to have a separate issue for actually implementing the changes and keep this simply for adding a deprecation message and updating the documentation?

[dblock]

We want to have some pull requests :)

[dblock]

#167

[ajcrites]

Can this issue be closed?

[dblock]

Closed via #167.

Also @ajcrites you have committer access don't you. Just do what you think is right and we can argue about it later ;)